Xen devel - Nov 2005 - question about disk performance in domU

Hi all,

When I ran the experiments to compare an application''s execution time
in both a domU (named cctest1)
and a native Linux machine (named ccn10), I noticed the application executes
faster in domU. The
host of the domU (named ccn9) and ccn10 are two nodes of a cluster and they have
same hardware
configurations. domU (cctest1) is created by exporting loopback files from dom0
on ccn9 as VBD
backends. The application execution logs there might be some disk I/O difference
between cctest and
ccn10, so I did some disk performance profiling with "hdparms" on
cctest1 (domU), ccn10 (native
Linux), ccn9 (dom0), and ccn9 (native Linux). Also, I checked the
"DMA" config information from the
output of dmesg. I tried to run "hdparm -i" and "hdparm -I"
but they didn''t work. Seems they didn''t
work with SCSI disks. The following are the results.
Thanks in advance for your help.
Best,
Xuehai

1. cctest1 (dumU)
**************************************************************************************************
cctest1$ df -lh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             1.5G  1.1G  306M  78% /
tmpfs                  62M  4.0K   62M   1% /dev/shm
/dev/sda6             4.2G  3.6G  453M  89% /tmp
/dev/sda5             938M  205M  685M  23% /var

cctest1$ dmesg | grep DMA
   DMA zone: 101376 pages, LIFO batch:16

cctest1$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done

  Timing cached reads:   512 MB in  2.00 seconds = 256.00 MB/sec
  Timing buffered disk reads:   44 MB in  3.00 seconds =  14.67 MB/sec

  Timing cached reads:   528 MB in  2.01 seconds = 262.69 MB/sec
  Timing buffered disk reads:   84 MB in  3.08 seconds =  27.27 MB/sec

  Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
  Timing buffered disk reads:  120 MB in  3.06 seconds =  39.22 MB/sec

  Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
  Timing buffered disk reads:  150 MB in  3.06 seconds =  49.02 MB/sec

  Timing cached reads:   536 MB in  2.00 seconds = 268.00 MB/sec
  Timing buffered disk reads:  178 MB in  3.17 seconds =  56.15 MB/sec

  Timing cached reads:   536 MB in  2.00 seconds = 268.00 MB/sec
  Timing buffered disk reads:  204 MB in  3.08 seconds =  66.23 MB/sec

  Timing cached reads:   532 MB in  2.00 seconds = 266.00 MB/sec
  Timing buffered disk reads:  228 MB in  3.13 seconds =  72.84 MB/sec

  Timing cached reads:   540 MB in  2.01 seconds = 268.66 MB/sec
  Timing buffered disk reads:  248 MB in  3.04 seconds =  81.58 MB/sec

  Timing cached reads:   540 MB in  2.00 seconds = 270.00 MB/sec
  Timing buffered disk reads:  266 MB in  3.06 seconds =  86.93 MB/sec

  Timing cached reads:   532 MB in  2.00 seconds = 266.00 MB/sec
  Timing buffered disk reads:  282 MB in  3.06 seconds =  92.16 MB/sec

**************************************************************************************************


2. ccn10 (native Linux)

**************************************************************************************************

ccn10$ df -lh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             1.5G  1.3G  149M  90% /
tmpfs                 252M     0  252M   0% /dev/shm
/dev/sda6             4.2G  3.6G  358M  92% /tmp
/dev/sda5             938M  706M  184M  80% /var

ccn10$ dmesg | grep DMA
   DMA zone: 4096 pages, LIFO batch:1

ccn10$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done

  Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
  Timing buffered disk reads:   62 MB in  3.03 seconds =  20.47 MB/sec

  Timing cached reads:   524 MB in  2.01 seconds = 261.00 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 257.65 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec

  Timing cached reads:   524 MB in  2.00 seconds = 262.04 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
  Timing buffered disk reads:   62 MB in  3.02 seconds =  20.51 MB/sec

  Timing cached reads:   524 MB in  2.00 seconds = 261.78 MB/sec
  Timing buffered disk reads:   62 MB in  3.02 seconds =  20.52 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
  Timing buffered disk reads:   62 MB in  3.02 seconds =  20.51 MB/sec

  Timing cached reads:   524 MB in  2.00 seconds = 261.78 MB/sec
  Timing buffered disk reads:   62 MB in  3.02 seconds =  20.50 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 257.40 MB/sec
  Timing buffered disk reads:   64 MB in  3.09 seconds =  20.73 MB/sec

  Timing cached reads:   524 MB in  2.01 seconds = 260.87 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec

**************************************************************************************************


3. ccn9 (dom0)
**************************************************************************************************

ccn9$ df -lh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             1.5G  1.1G  306M  78% /
tmpfs                  62M  4.0K   62M   1% /dev/shm
/dev/sda6             4.2G  3.6G  453M  89% /tmp
/dev/sda5             938M  205M  685M  23% /var

ccn9$ dmesg | grep DMA
   DMA zone: 32768 pages, LIFO batch:8

ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done

  Timing cached reads:   504 MB in  2.00 seconds = 252.00 MB/sec
  Timing buffered disk reads:   60 MB in  3.14 seconds =  19.11 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
  Timing buffered disk reads:   62 MB in  3.15 seconds =  19.68 MB/sec

  Timing cached reads:   512 MB in  2.00 seconds = 256.00 MB/sec
  Timing buffered disk reads:   60 MB in  3.08 seconds =  19.48 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
  Timing buffered disk reads:   58 MB in  3.02 seconds =  19.21 MB/sec

  Timing cached reads:   516 MB in  2.01 seconds = 256.72 MB/sec
  Timing buffered disk reads:   60 MB in  3.12 seconds =  19.23 MB/sec

  Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
  Timing buffered disk reads:   60 MB in  3.13 seconds =  19.17 MB/sec

  Timing cached reads:   520 MB in  2.01 seconds = 258.71 MB/sec
  Timing buffered disk reads:   60 MB in  3.13 seconds =  19.17 MB/sec

  Timing cached reads:   520 MB in  2.01 seconds = 258.71 MB/sec
  Timing buffered disk reads:   60 MB in  3.06 seconds =  19.61 MB/sec

  Timing cached reads:   516 MB in  2.01 seconds = 256.72 MB/sec
  Timing buffered disk reads:   60 MB in  3.14 seconds =  19.11 MB/sec

  Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
  Timing buffered disk reads:   60 MB in  3.15 seconds =  19.05 MB/sec

**************************************************************************************************

4. ccn9 (native Linux)
**************************************************************************************************
ccn9$ df -lh
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             1.5G  1.1G  306M  78% /
tmpfs                  62M  4.0K   62M   1% /dev/shm
/dev/sda6             4.2G  3.6G  453M  89% /tmp
/dev/sda5             938M  205M  685M  23% /var

ccn9 $ dmesg | grep DMA
   DMA zone: 4096 pages, LIFO batch:1

ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
/dev/sda1:
  Timing cached reads:   492 MB in  2.01 seconds = 244.57 MB/sec
  Timing buffered disk reads:   62 MB in  3.10 seconds =  20.01 MB/sec

  Timing cached reads:   484 MB in  2.01 seconds = 241.07 MB/sec
  Timing buffered disk reads:   48 MB in  3.01 seconds =  15.95 MB/sec

  Timing cached reads:   484 MB in  2.00 seconds = 241.67 MB/sec
  Timing buffered disk reads:   62 MB in  3.03 seconds =  20.45 MB/sec

  Timing cached reads:   484 MB in  2.01 seconds = 241.31 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.57 MB/sec

  Timing cached reads:   480 MB in  2.01 seconds = 239.08 MB/sec
  Timing buffered disk reads:   62 MB in  3.03 seconds =  20.49 MB/sec

  Timing cached reads:   488 MB in  2.01 seconds = 243.31 MB/sec
  Timing buffered disk reads:   62 MB in  3.05 seconds =  20.31 MB/sec

  Timing cached reads:   484 MB in  2.01 seconds = 241.31 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec

  Timing cached reads:   484 MB in  2.00 seconds = 241.67 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.59 MB/sec

  Timing cached reads:   488 MB in  2.01 seconds = 242.34 MB/sec
  Timing buffered disk reads:   62 MB in  3.01 seconds =  20.59 MB/sec

  Timing cached reads:   484 MB in  2.01 seconds = 240.35 MB/sec
  Timing buffered disk reads:   62 MB in  3.09 seconds =  20.09 MB/sec
**************************************************************************************************

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So the "Timing buffered disk reads" show much higher results.  I see
the DMA
zone is larger in domU, but since this is mapped to a loopback file I''m
guessing
the physical disk performance should only be affected by what dom0''s
DMA zone is
set to on the node running the domU if that is all that was going on.  But dom0
performance seems comparable to native linux. 

Is this huge "timing buffered disk read" difference accurate? Does the
domU
benefit from some other cache of the loopback file in dom0?  How does the DMA
setting in domU work?

Thanks for any insights,
Tim 

On Mon, 21 Nov 2005 09:41:08 -0600
xuehai zhang <hai@cs.uchicago.edu> wrote:
> Hi all,
> 
> When I ran the experiments to compare an application''s execution
time in both
> a domU (named cctest1)  and a native Linux machine (named ccn10), I noticed
> the application executes faster in domU. The  host of the domU (named ccn9)
> and ccn10 are two nodes of a cluster and they have same hardware 
> configurations. domU (cctest1) is created by exporting loopback files from
> dom0 on ccn9 as VBD  backends. The application execution logs there might
be
> some disk I/O difference between cctest and  ccn10, so I did some disk
> performance profiling with "hdparms" on cctest1 (domU), ccn10
(native  Linux),
> ccn9 (dom0), and ccn9 (native Linux). Also, I checked the "DMA"
config
> information from the  output of dmesg. I tried to run "hdparm -i"
and "hdparm
> -I" but they didn''t work. Seems they didn''t  work
with SCSI disks. The
> following are the results. Thanks in advance for your help.
> Best,
> Xuehai
> 
> 1. cctest1 (dumU)
>
*****************************************************************************
> ********************* cctest1$ df -lh
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1             1.5G  1.1G  306M  78% /
> tmpfs                  62M  4.0K   62M   1% /dev/shm
> /dev/sda6             4.2G  3.6G  453M  89% /tmp
> /dev/sda5             938M  205M  685M  23% /var
> 
> cctest1$ dmesg | grep DMA
>    DMA zone: 101376 pages, LIFO batch:16
> 
> cctest1$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
> 
>   Timing cached reads:   512 MB in  2.00 seconds = 256.00 MB/sec
>   Timing buffered disk reads:   44 MB in  3.00 seconds =  14.67 MB/sec
> 
>   Timing cached reads:   528 MB in  2.01 seconds = 262.69 MB/sec
>   Timing buffered disk reads:   84 MB in  3.08 seconds =  27.27 MB/sec
> 
>   Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
>   Timing buffered disk reads:  120 MB in  3.06 seconds =  39.22 MB/sec
> 
>   Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
>   Timing buffered disk reads:  150 MB in  3.06 seconds =  49.02 MB/sec
> 
>   Timing cached reads:   536 MB in  2.00 seconds = 268.00 MB/sec
>   Timing buffered disk reads:  178 MB in  3.17 seconds =  56.15 MB/sec
> 
>   Timing cached reads:   536 MB in  2.00 seconds = 268.00 MB/sec
>   Timing buffered disk reads:  204 MB in  3.08 seconds =  66.23 MB/sec
> 
>   Timing cached reads:   532 MB in  2.00 seconds = 266.00 MB/sec
>   Timing buffered disk reads:  228 MB in  3.13 seconds =  72.84 MB/sec
> 
>   Timing cached reads:   540 MB in  2.01 seconds = 268.66 MB/sec
>   Timing buffered disk reads:  248 MB in  3.04 seconds =  81.58 MB/sec
> 
>   Timing cached reads:   540 MB in  2.00 seconds = 270.00 MB/sec
>   Timing buffered disk reads:  266 MB in  3.06 seconds =  86.93 MB/sec
> 
>   Timing cached reads:   532 MB in  2.00 seconds = 266.00 MB/sec
>   Timing buffered disk reads:  282 MB in  3.06 seconds =  92.16 MB/sec
> 
>
*****************************************************************************
> *********************
> 
> 
> 2. ccn10 (native Linux)
> 
>
*****************************************************************************
> *********************
> 
> ccn10$ df -lh
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1             1.5G  1.3G  149M  90% /
> tmpfs                 252M     0  252M   0% /dev/shm
> /dev/sda6             4.2G  3.6G  358M  92% /tmp
> /dev/sda5             938M  706M  184M  80% /var
> 
> ccn10$ dmesg | grep DMA
>    DMA zone: 4096 pages, LIFO batch:1
> 
> ccn10$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
>   Timing buffered disk reads:   62 MB in  3.03 seconds =  20.47 MB/sec
> 
>   Timing cached reads:   524 MB in  2.01 seconds = 261.00 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 257.65 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec
> 
>   Timing cached reads:   524 MB in  2.00 seconds = 262.04 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
>   Timing buffered disk reads:   62 MB in  3.02 seconds =  20.51 MB/sec
> 
>   Timing cached reads:   524 MB in  2.00 seconds = 261.78 MB/sec
>   Timing buffered disk reads:   62 MB in  3.02 seconds =  20.52 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
>   Timing buffered disk reads:   62 MB in  3.02 seconds =  20.51 MB/sec
> 
>   Timing cached reads:   524 MB in  2.00 seconds = 261.78 MB/sec
>   Timing buffered disk reads:   62 MB in  3.02 seconds =  20.50 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 257.40 MB/sec
>   Timing buffered disk reads:   64 MB in  3.09 seconds =  20.73 MB/sec
> 
>   Timing cached reads:   524 MB in  2.01 seconds = 260.87 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec
> 
>
*****************************************************************************
> *********************
> 
> 
> 3. ccn9 (dom0)
>
*****************************************************************************
> *********************
> 
> ccn9$ df -lh
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1             1.5G  1.1G  306M  78% /
> tmpfs                  62M  4.0K   62M   1% /dev/shm
> /dev/sda6             4.2G  3.6G  453M  89% /tmp
> /dev/sda5             938M  205M  685M  23% /var
> 
> ccn9$ dmesg | grep DMA
>    DMA zone: 32768 pages, LIFO batch:8
> 
> ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
> 
>   Timing cached reads:   504 MB in  2.00 seconds = 252.00 MB/sec
>   Timing buffered disk reads:   60 MB in  3.14 seconds =  19.11 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
>   Timing buffered disk reads:   62 MB in  3.15 seconds =  19.68 MB/sec
> 
>   Timing cached reads:   512 MB in  2.00 seconds = 256.00 MB/sec
>   Timing buffered disk reads:   60 MB in  3.08 seconds =  19.48 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
>   Timing buffered disk reads:   58 MB in  3.02 seconds =  19.21 MB/sec
> 
>   Timing cached reads:   516 MB in  2.01 seconds = 256.72 MB/sec
>   Timing buffered disk reads:   60 MB in  3.12 seconds =  19.23 MB/sec
> 
>   Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
>   Timing buffered disk reads:   60 MB in  3.13 seconds =  19.17 MB/sec
> 
>   Timing cached reads:   520 MB in  2.01 seconds = 258.71 MB/sec
>   Timing buffered disk reads:   60 MB in  3.13 seconds =  19.17 MB/sec
> 
>   Timing cached reads:   520 MB in  2.01 seconds = 258.71 MB/sec
>   Timing buffered disk reads:   60 MB in  3.06 seconds =  19.61 MB/sec
> 
>   Timing cached reads:   516 MB in  2.01 seconds = 256.72 MB/sec
>   Timing buffered disk reads:   60 MB in  3.14 seconds =  19.11 MB/sec
> 
>   Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
>   Timing buffered disk reads:   60 MB in  3.15 seconds =  19.05 MB/sec
> 
>
*****************************************************************************
> *********************
> 
> 4. ccn9 (native Linux)
>
*****************************************************************************
> ********************* ccn9$ df -lh
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1             1.5G  1.1G  306M  78% /
> tmpfs                  62M  4.0K   62M   1% /dev/shm
> /dev/sda6             4.2G  3.6G  453M  89% /tmp
> /dev/sda5             938M  205M  685M  23% /var
> 
> ccn9 $ dmesg | grep DMA
>    DMA zone: 4096 pages, LIFO batch:1
> 
> ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
> /dev/sda1:
>   Timing cached reads:   492 MB in  2.01 seconds = 244.57 MB/sec
>   Timing buffered disk reads:   62 MB in  3.10 seconds =  20.01 MB/sec
> 
>   Timing cached reads:   484 MB in  2.01 seconds = 241.07 MB/sec
>   Timing buffered disk reads:   48 MB in  3.01 seconds =  15.95 MB/sec
> 
>   Timing cached reads:   484 MB in  2.00 seconds = 241.67 MB/sec
>   Timing buffered disk reads:   62 MB in  3.03 seconds =  20.45 MB/sec
> 
>   Timing cached reads:   484 MB in  2.01 seconds = 241.31 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.57 MB/sec
> 
>   Timing cached reads:   480 MB in  2.01 seconds = 239.08 MB/sec
>   Timing buffered disk reads:   62 MB in  3.03 seconds =  20.49 MB/sec
> 
>   Timing cached reads:   488 MB in  2.01 seconds = 243.31 MB/sec
>   Timing buffered disk reads:   62 MB in  3.05 seconds =  20.31 MB/sec
> 
>   Timing cached reads:   484 MB in  2.01 seconds = 241.31 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.61 MB/sec
> 
>   Timing cached reads:   484 MB in  2.00 seconds = 241.67 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.59 MB/sec
> 
>   Timing cached reads:   488 MB in  2.01 seconds = 242.34 MB/sec
>   Timing buffered disk reads:   62 MB in  3.01 seconds =  20.59 MB/sec
> 
>   Timing cached reads:   484 MB in  2.01 seconds = 240.35 MB/sec
>   Timing buffered disk reads:   62 MB in  3.09 seconds =  20.09 MB/sec
>
*****************************************************************************
> *********************
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 
_______________________________________________
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http://lists.xensource.com/xen-devel

>> -----Original Message-----
>> From: xen-devel-bounces@lists.xensource.com 
>> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
>> Tim Freeman
>> Sent: Monday, November 21, 2005 12:45 PM
>> To: xen-devel@lists.xensource.com
>> Cc: keahey@mcs.anl.gov; xuehai zhang
>> Subject: Re: [Xen-devel] question about disk performance in domU
>> 
>> 
>> So the "Timing buffered disk reads" show much higher 
>> results.  I see the DMA zone is larger in domU, but since 
>> this is mapped to a loopback file I''m guessing the physical 
>> disk performance should only be affected by what dom0''s DMA 
>> zone is set to on the node running the domU if that is all 
>> that was going on.  But dom0 performance seems comparable to 
>> native linux. 
>> 
>> Is this huge "timing buffered disk read" difference 
>> accurate? Does the domU benefit from some other cache of the 
>> loopback file in dom0?  
 
  Yes. It seems to me that this is the effect of the file buffer
  cache on dom0. hdparm flushes the file cache on domU 
  to make sure that there is no data in the file buffer cache 
  when measuring device access times (reported as buffered disk
  reads). However when  using VBDs mapped to files, the data is
  also cached on dom0 file buffer. Therefore data is not coming
  directly from the device but from dom0 file cache. Note how the 
  amount of data that is read in 3 sec increases at each step,
  since data read in previous steps come from dom0 file cache.
 
  Regards

  Renato


>> Thanks for any insights,
>> Tim 
>> 
>> On Mon, 21 Nov 2005 09:41:08 -0600
>> xuehai zhang <hai@cs.uchicago.edu> wrote:
>> 
>> > Hi all,
>> > 
>> > When I ran the experiments to compare an application''s 
>> execution time 
>> > in both a domU (named cctest1)  and a native Linux machine (named 
>> > ccn10), I noticed the application executes faster in domU. 
>> The  host 
>> > of the domU (named ccn9) and ccn10 are two nodes of a 
>> cluster and they 
>> > have same hardware configurations. domU (cctest1) is created by 
>> > exporting loopback files from dom0 on ccn9 as VBD  backends. The 
>> > application execution logs there might be some disk I/O difference
>> > between cctest and  ccn10, so I did some disk performance 
>> profiling 
>> > with "hdparms" on cctest1 (domU), ccn10 (native  Linux),
>> ccn9 (dom0), 
>> > and ccn9 (native Linux). Also, I checked the "DMA"
config
>> information 
>> > from the  output of dmesg. I tried to run "hdparm -i"
and
>> "hdparm -I" 
>> > but they didn''t work. Seems they didn''t  work
with SCSI disks. The
>> > following are the results. Thanks in advance for your help. Best, 
>> > Xuehai
>> > 
>> > 1. cctest1 (dumU)
>> > 
>> *************************************************************
>> *********
>> > *******
>> > ********************* cctest1$ df -lh
>> > Filesystem            Size  Used Avail Use% Mounted on
>> > /dev/sda1             1.5G  1.1G  306M  78% /
>> > tmpfs                  62M  4.0K   62M   1% /dev/shm
>> > /dev/sda6             4.2G  3.6G  453M  89% /tmp
>> > /dev/sda5             938M  205M  685M  23% /var
>> > 
>> > cctest1$ dmesg | grep DMA
>> >    DMA zone: 101376 pages, LIFO batch:16
>> > 
>> > cctest1$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>> > 
>> >   Timing cached reads:   512 MB in  2.00 seconds = 256.00 MB/sec
>> >   Timing buffered disk reads:   44 MB in  3.00 seconds =  
>> 14.67 MB/sec
>> > 
>> >   Timing cached reads:   528 MB in  2.01 seconds = 262.69 MB/sec
>> >   Timing buffered disk reads:   84 MB in  3.08 seconds =  
>> 27.27 MB/sec
>> > 
>> >   Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
>> >   Timing buffered disk reads:  120 MB in  3.06 seconds =  
>> 39.22 MB/sec
>> > 
>> >   Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
>> >   Timing buffered disk reads:  150 MB in  3.06 seconds =  
>> 49.02 MB/sec
>> > 
>> >   Timing cached reads:   536 MB in  2.00 seconds = 268.00 MB/sec
>> >   Timing buffered disk reads:  178 MB in  3.17 seconds =  
>> 56.15 MB/sec
>> > 
>> >   Timing cached reads:   536 MB in  2.00 seconds = 268.00 MB/sec
>> >   Timing buffered disk reads:  204 MB in  3.08 seconds =  
>> 66.23 MB/sec
>> > 
>> >   Timing cached reads:   532 MB in  2.00 seconds = 266.00 MB/sec
>> >   Timing buffered disk reads:  228 MB in  3.13 seconds =  
>> 72.84 MB/sec
>> > 
>> >   Timing cached reads:   540 MB in  2.01 seconds = 268.66 MB/sec
>> >   Timing buffered disk reads:  248 MB in  3.04 seconds =  
>> 81.58 MB/sec
>> > 
>> >   Timing cached reads:   540 MB in  2.00 seconds = 270.00 MB/sec
>> >   Timing buffered disk reads:  266 MB in  3.06 seconds =  
>> 86.93 MB/sec
>> > 
>> >   Timing cached reads:   532 MB in  2.00 seconds = 266.00 MB/sec
>> >   Timing buffered disk reads:  282 MB in  3.06 seconds =  
>> 92.16 MB/sec
>> > 
>> > 
>> *************************************************************
>> *********
>> > *******
>> > *********************
>> > 
>> > 
>> > 2. ccn10 (native Linux)
>> > 
>> > 
>> *************************************************************
>> *********
>> > *******
>> > *********************
>> > 
>> > ccn10$ df -lh
>> > Filesystem            Size  Used Avail Use% Mounted on
>> > /dev/sda1             1.5G  1.3G  149M  90% /
>> > tmpfs                 252M     0  252M   0% /dev/shm
>> > /dev/sda6             4.2G  3.6G  358M  92% /tmp
>> > /dev/sda5             938M  706M  184M  80% /var
>> > 
>> > ccn10$ dmesg | grep DMA
>> >    DMA zone: 4096 pages, LIFO batch:1
>> > 
>> > ccn10$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.03 seconds =  
>> 20.47 MB/sec
>> > 
>> >   Timing cached reads:   524 MB in  2.01 seconds = 261.00 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.61 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 257.65 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.61 MB/sec
>> > 
>> >   Timing cached reads:   524 MB in  2.00 seconds = 262.04 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.61 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.02 seconds =  
>> 20.51 MB/sec
>> > 
>> >   Timing cached reads:   524 MB in  2.00 seconds = 261.78 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.02 seconds =  
>> 20.52 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 257.78 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.02 seconds =  
>> 20.51 MB/sec
>> > 
>> >   Timing cached reads:   524 MB in  2.00 seconds = 261.78 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.02 seconds =  
>> 20.50 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 257.40 MB/sec
>> >   Timing buffered disk reads:   64 MB in  3.09 seconds =  
>> 20.73 MB/sec
>> > 
>> >   Timing cached reads:   524 MB in  2.01 seconds = 260.87 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.61 MB/sec
>> > 
>> > 
>> *************************************************************
>> *********
>> > *******
>> > *********************
>> > 
>> > 
>> > 3. ccn9 (dom0)
>> > 
>> *************************************************************
>> *********
>> > *******
>> > *********************
>> > 
>> > ccn9$ df -lh
>> > Filesystem            Size  Used Avail Use% Mounted on
>> > /dev/sda1             1.5G  1.1G  306M  78% /
>> > tmpfs                  62M  4.0K   62M   1% /dev/shm
>> > /dev/sda6             4.2G  3.6G  453M  89% /tmp
>> > /dev/sda5             938M  205M  685M  23% /var
>> > 
>> > ccn9$ dmesg | grep DMA
>> >    DMA zone: 32768 pages, LIFO batch:8
>> > 
>> > ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>> > 
>> >   Timing cached reads:   504 MB in  2.00 seconds = 252.00 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.14 seconds =  
>> 19.11 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.15 seconds =  
>> 19.68 MB/sec
>> > 
>> >   Timing cached reads:   512 MB in  2.00 seconds = 256.00 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.08 seconds =  
>> 19.48 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
>> >   Timing buffered disk reads:   58 MB in  3.02 seconds =  
>> 19.21 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.01 seconds = 256.72 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.12 seconds =  
>> 19.23 MB/sec
>> > 
>> >   Timing cached reads:   520 MB in  2.00 seconds = 260.00 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.13 seconds =  
>> 19.17 MB/sec
>> > 
>> >   Timing cached reads:   520 MB in  2.01 seconds = 258.71 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.13 seconds =  
>> 19.17 MB/sec
>> > 
>> >   Timing cached reads:   520 MB in  2.01 seconds = 258.71 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.06 seconds =  
>> 19.61 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.01 seconds = 256.72 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.14 seconds =  
>> 19.11 MB/sec
>> > 
>> >   Timing cached reads:   516 MB in  2.00 seconds = 258.00 MB/sec
>> >   Timing buffered disk reads:   60 MB in  3.15 seconds =  
>> 19.05 MB/sec
>> > 
>> > 
>> *************************************************************
>> *********
>> > *******
>> > *********************
>> > 
>> > 4. ccn9 (native Linux)
>> > 
>> *************************************************************
>> *********
>> > *******
>> > ********************* ccn9$ df -lh
>> > Filesystem            Size  Used Avail Use% Mounted on
>> > /dev/sda1             1.5G  1.1G  306M  78% /
>> > tmpfs                  62M  4.0K   62M   1% /dev/shm
>> > /dev/sda6             4.2G  3.6G  453M  89% /tmp
>> > /dev/sda5             938M  205M  685M  23% /var
>> > 
>> > ccn9 $ dmesg | grep DMA
>> >    DMA zone: 4096 pages, LIFO batch:1
>> > 
>> > ccn9$ for i in `seq 1 10`; do hdparm -tT /dev/sda1; done
>> > /dev/sda1:
>> >   Timing cached reads:   492 MB in  2.01 seconds = 244.57 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.10 seconds =  
>> 20.01 MB/sec
>> > 
>> >   Timing cached reads:   484 MB in  2.01 seconds = 241.07 MB/sec
>> >   Timing buffered disk reads:   48 MB in  3.01 seconds =  
>> 15.95 MB/sec
>> > 
>> >   Timing cached reads:   484 MB in  2.00 seconds = 241.67 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.03 seconds =  
>> 20.45 MB/sec
>> > 
>> >   Timing cached reads:   484 MB in  2.01 seconds = 241.31 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.57 MB/sec
>> > 
>> >   Timing cached reads:   480 MB in  2.01 seconds = 239.08 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.03 seconds =  
>> 20.49 MB/sec
>> > 
>> >   Timing cached reads:   488 MB in  2.01 seconds = 243.31 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.05 seconds =  
>> 20.31 MB/sec
>> > 
>> >   Timing cached reads:   484 MB in  2.01 seconds = 241.31 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.61 MB/sec
>> > 
>> >   Timing cached reads:   484 MB in  2.00 seconds = 241.67 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.59 MB/sec
>> > 
>> >   Timing cached reads:   488 MB in  2.01 seconds = 242.34 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.01 seconds =  
>> 20.59 MB/sec
>> > 
>> >   Timing cached reads:   484 MB in  2.01 seconds = 240.35 MB/sec
>> >   Timing buffered disk reads:   62 MB in  3.09 seconds =  
>> 20.09 MB/sec
>> > 
>> *************************************************************
>> *********
>> > *******
>> > *********************
>> > 
>> > _______________________________________________
>> > Xen-devel mailing list
>> > Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
>> > 
>> 
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
>> 
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Renato and Tim,
Thank you for your replies.
Is there anyway to flush the dom0 file buffer before running hdparm on domU each
time?
Xuehai

Santos, Jose Renato G wrote:
> 
>>>-----Original Message-----
>>>From: xen-devel-bounces@lists.xensource.com 
>>>[mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of 
>>>Tim Freeman
>>>Sent: Monday, November 21, 2005 12:45 PM
>>>To: xen-devel@lists.xensource.com
>>>Cc: keahey@mcs.anl.gov; xuehai zhang
>>>Subject: Re: [Xen-devel] question about disk performance in domU
>>>
>>>
>>>So the "Timing buffered disk reads" show much higher 
>>>results.  I see the DMA zone is larger in domU, but since 
>>>this is mapped to a loopback file I''m guessing the physical
>>>disk performance should only be affected by what dom0''s DMA
>>>zone is set to on the node running the domU if that is all 
>>>that was going on.  But dom0 performance seems comparable to 
>>>native linux. 
>>>
>>>Is this huge "timing buffered disk read" difference 
>>>accurate? Does the domU benefit from some other cache of the 
>>>loopback file in dom0?  
> 
>  
>   Yes. It seems to me that this is the effect of the file buffer
>   cache on dom0. hdparm flushes the file cache on domU 
>   to make sure that there is no data in the file buffer cache 
>   when measuring device access times (reported as buffered disk
>   reads). However when  using VBDs mapped to files, the data is
>   also cached on dom0 file buffer. Therefore data is not coming
>   directly from the device but from dom0 file cache. Note how the 
>   amount of data that is read in 3 sec increases at each step,
>   since data read in previous steps come from dom0 file cache.
>  
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On Mon, 21 Nov 2005, xuehai zhang wrote:
> Renato and Tim,
> Thank you for your replies.
> Is there anyway to flush the dom0 file buffer before running hdparm on domU
each time?
hdparm calls an ioctl to flush it.  Maybe that should be passed thru.

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Adam,
I don''t know much about how hdparm really works. Are you suggesting
dom0''s file buffer cache should
be flushed by default every time because hdparm calls an ioctl to flush? If it
is not the case, how
does the data used by hdparm in domU get into the dom0''s file buffer
cache in the 1st run?
Thanks.
Xuehai

Adam Heath wrote:
> On Mon, 21 Nov 2005, xuehai zhang wrote:
> 
> 
>>Renato and Tim,
>>Thank you for your replies.
>>Is there anyway to flush the dom0 file buffer before running hdparm on
domU each time?
> 
> 
> hdparm calls an ioctl to flush it.  Maybe that should be passed thru.
> 

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