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Ian Pratt

2006-Nov-07 18:45 UTC

RE: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

> Attached is the diff of the two kernel configs.
There are a *lot* of differences between those kernel configs. A cursory
glance spots such gems as:

< CONFIG_DEFAULT_IOSCHED="cfq"
---> CONFIG_DEFAULT_IOSCHED="anticipatory"
All bets are off.

Ian

 > ----- Original Message -----
> From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> To: "Liang Yang" <yangliang_mr@hotmail.com>; "John
Byrne"
> <john.l.byrne@hp.com>
> Cc: "xen-devel" <xen-devel@lists.xensource.com>;
"Emmanuel Ackaouy"
> <ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
> Sent: Tuesday, November 07, 2006 11:15 AM
> Subject: RE: Performance data of Linux native vs. Xen Dom0 
> and Xen DomU. Re: 
> [Xen-devel] Direct I/O to domU seeing a 30% performance hit
> 
> 
> > I already set dom0_max_vcpus=1 for domain0 when I was doing testing.
> Also,
> > Linux native kernel and domU kernel are all compiled as 
> Uni-Processor
> > mode.All the testing for Linux native, domain0 and domainU 
> are exactly
> the
> > same. All used Linux kernel 2.6.16.29.
> 
> Please could you post a ''diff'' of the two kernel configs.
> 
> It might be worth diff''ing the boot messages in both cases too.
> 
> Thanks,
> Ian
> 
> 
> > Regards,
> >
> > Liang
> >
> > ----- Original Message -----
> > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > To: "Liang Yang" <multisyncfe991@hotmail.com>;
"John Byrne"
> > <john.l.byrne@hp.com>
> > Cc: "xen-devel" <xen-devel@lists.xensource.com>;
"Emmanuel Ackaouy"
> > <ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
> > Sent: Tuesday, November 07, 2006 11:06 AM
> > Subject: RE: Performance data of Linux native vs. Xen Dom0 and Xen
> DomU.
> > Re:
> > [Xen-devel] Direct I/O to domU seeing a 30% performance hit
> >
> >
> > > I''m also doing some performance analysis about Linux
native, dom0
> and
> > domU
> > > (para-virtualized). Here are some brief comparison for 256K
> sequential
> > > read/write. The testing is done using for JBOD based on 8 
> Maxtor SAS
> > Atlas
> > > 2
> > > 15K drives with LSI SAS HBA.
> > >
> > > 256K Sequential Read
> > > Linux Native: 559.6MB/s
> > > Xen Domain0: 423.3MB/s
> > > Xen DomainU: 555.9MB/s
> >
> > This doesn''t make a lot of sense. Only thing I can think of
is that
> > there must be some extra prefetching going on in the domU case. It
> still
> > doesn''t explain why the dom0 result is so much worse than
native.
> >
> > It might be worth repeating with both native and dom0 boot with
> > maxcpus=1.
> >
> > Are you using near-identical kernels in both cases? Same 
> drivers, same
> > part of the disk for the tests, etc?
> >
> > How are you doing the measurement? A timed ''dd''?
> >
> > Ian
> >
> >
> > > 256K Sequential Write
> > > Linux Native: 668.9MB/s
> > > Xen Domain0: 708.7MB/s
> > > Xen DomainU: 373.5MB/s
> > >
> > > Just two questions:
> > >
> > > It seems para-virtualized DomU outperform Dom0 in terms of
> sequential
> > read
> > > and is very to Linux native performance. However, DomU does show
> poor
> > (only
> > > 50%) sequential write performance compared with Linux native and
> Dom0.
> > >
> > > Could you explain some reason behind this?
> > >
> > > Thanks,
> > >
> > > Liang
> > >
> > >
> > > ----- Original Message -----
> > > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > > To: "John Byrne" <john.l.byrne@hp.com>
> > > Cc: "xen-devel" <xen-devel@lists.xensource.com>; 
> "Emmanuel Ackaouy"
> > > <ack@xensource.com>
> > > Sent: Tuesday, November 07, 2006 10:20 AM
> > > Subject: RE: [Xen-devel] Direct I/O to domU seeing a 30% 
> performance
> > hit
> > >
> > >
> > > > Both dom0 and the domU are SLES 10, so I don''t know
why
> the "idle"
> > > > performance of the two should be different. The obvious 
> asymmetry
> is
> > > the
> > > > disk. Since the disk isn''t direct, any disk I/O by
the
> domU would
> > > > certainly impact dom0, but I don''t think there
should
> be much, if
> > any.
> > > I
> > > > did run a dom0 test with the domU started, but idle and 
> there was
> no
> > > > real change to dom0''s numbers.
> > > >
> > > > What''s the best way to gather information about
what is going on
> > with
> > > > the domains without perturbing them? (Or, at least,
perturbing
> > > everyone
> > > > equally.)
> > > >
> > > > As to the test, I am running netperf 2.4.1 on an outside
machine
> to
> > > the
> > > > dom0 and the domU. (So the doms are running the netserver
> portion.)
> > I
> > > > was originally running it in the doms to the outside 
> machine, but
> > when
> > > > the bad numbers showed up I moved it to the outside machine
> because
> > I
> > > > wondered if the bad numbers were due to something 
> happening to the
> > > > system time in domU. The numbers is the "outside"
test to domU
> look
> > > worse.
> > >
> > >
> > > It might be worth checking that there''s no interrupt
sharing
> > happening.
> > > While running the test against the domU, see how much CPU 
> dom0 burns
> > in
> > > the same period using ''xm vcpu-list''.
> > >
> > > To keep things simple, have dom0 and domU as uniprocessor guests.
> > >
> > > Ian
> > >
> > >
> > > > Ian Pratt wrote:
> > > > >
> > > > >> There have been a couple of network receive
throughput
> > > > >> performance regressions to domUs over time that
were
> > > > >> subsequently fixed. I think one may have crept in
to 3.0.3.
> > > > >
> > > > > The report was (I believe) with a NIC directly assigned
to the
> > domU,
> > > so
> > > > > not using netfront/back at all.
> > > > >
> > > > > John: please can you give more details on your config.
> > > > >
> > > > > Ian
> > > > >
> > > > >> Are you seeing any dropped packets on the vif
associated with
> > > > >> your domU in your dom0? If so, propagating
changeset
> > > > >> 11861 from unstable may help:
> > > > >>
> > > > >> changeset:   11861:637eace6d5c6
> > > > >> user:        kfraser@localhost.localdomain
> > > > >> date:        Mon Oct 23 11:20:37 2006 +0100
> > > > >> summary:     [NET] back: Fix packet queuing so that
packets
> > > > >> are drained if the
> > > > >>
> > > > >>
> > > > >> In the past, we also had receive throughput issues
to domUs
> > > > >> that were due to socket buffer size logic but those
were
> > > > >> fixed a while ago.
> > > > >>
> > > > >> Can you send netstat -i output from dom0?
> > > > >>
> > > > >> Emmanuel.
> > > > >>
> > > > >>
> > > > >> On Mon, Nov 06, 2006 at 09:55:17PM -0800, John
Byrne wrote:
> > > > >>> I was asked to test direct I/O to a PV domU.
Since, I had a
> > system
> > > > >>> with two NICs, I gave one to a domU and one
dom0. (Each is
> > > > >> running the
> > > > >>> same
> > > > >>> kernel: xen 3.0.3 x86_64.)
> > > > >>>
> > > > >>> I''m running netperf from an outside
system to the domU and
> > > > >> dom0 and I
> > > > >>> am seeing 30% less throughput for the domU vs
dom0.
> > > > >>>
> > > > >>> Is this to be expected? If so, why? If not,
does anyone
> > > > >> have a guess
> > > > >>> as to what I might be doing wrong or what the
issue
> might be?
> > > > >>>
> > > > >>> Thanks,
> > > > >>>
> > > > >>> John Byrne
> > > > >> _______________________________________________
> > > > >> 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
> > > > >
> > >
> > >
> > > _______________________________________________
> > > 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

George Dunlap

2006-Nov-07 18:53 UTC

head link

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

One of the strange things, though, is that the difference should be so
big between domU and dom0, which are using the exact same same kernel
(correct me if I''m wrong).

I''m not familiar with the I/O scheduling.  Is it possible that the I/O
scheduling inside the domU is interacting poorly with the I/O
scheduling in dom0?  That''s one hypothesis for why domU writes are
slower than dom0 writes; but that doesn''t seem to explain why domU
reads would be *faster* than dom0 reads.

 -George

On 11/7/06, Ian Pratt <m+Ian.Pratt@cl.cam.ac.uk>
wrote:> > Attached is the diff of the two kernel configs.
>
> There are a *lot* of differences between those kernel configs. A cursory
> glance spots such gems as:
>
> < CONFIG_DEFAULT_IOSCHED="cfq"
> ---
> > CONFIG_DEFAULT_IOSCHED="anticipatory"
>
> All bets are off.
>
> Ian
>
>
> > ----- Original Message -----
> > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > To: "Liang Yang" <yangliang_mr@hotmail.com>;
"John Byrne"
> > <john.l.byrne@hp.com>
> > Cc: "xen-devel" <xen-devel@lists.xensource.com>;
"Emmanuel Ackaouy"
> > <ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
> > Sent: Tuesday, November 07, 2006 11:15 AM
> > Subject: RE: Performance data of Linux native vs. Xen Dom0
> > and Xen DomU. Re:
> > [Xen-devel] Direct I/O to domU seeing a 30% performance hit
> >
> >
> > > I already set dom0_max_vcpus=1 for domain0 when I was doing
testing.
> > Also,
> > > Linux native kernel and domU kernel are all compiled as
> > Uni-Processor
> > > mode.All the testing for Linux native, domain0 and domainU
> > are exactly
> > the
> > > same. All used Linux kernel 2.6.16.29.
> >
> > Please could you post a ''diff'' of the two kernel
configs.
> >
> > It might be worth diff''ing the boot messages in both cases
too.
> >
> > Thanks,
> > Ian
> >
> >
> > > Regards,
> > >
> > > Liang
> > >
> > > ----- Original Message -----
> > > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > > To: "Liang Yang" <multisyncfe991@hotmail.com>;
"John Byrne"
> > > <john.l.byrne@hp.com>
> > > Cc: "xen-devel" <xen-devel@lists.xensource.com>;
"Emmanuel Ackaouy"
> > > <ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
> > > Sent: Tuesday, November 07, 2006 11:06 AM
> > > Subject: RE: Performance data of Linux native vs. Xen Dom0 and
Xen
> > DomU.
> > > Re:
> > > [Xen-devel] Direct I/O to domU seeing a 30% performance hit
> > >
> > >
> > > > I''m also doing some performance analysis about
Linux native, dom0
> > and
> > > domU
> > > > (para-virtualized). Here are some brief comparison for 256K
> > sequential
> > > > read/write. The testing is done using for JBOD based on 8
> > Maxtor SAS
> > > Atlas
> > > > 2
> > > > 15K drives with LSI SAS HBA.
> > > >
> > > > 256K Sequential Read
> > > > Linux Native: 559.6MB/s
> > > > Xen Domain0: 423.3MB/s
> > > > Xen DomainU: 555.9MB/s
> > >
> > > This doesn''t make a lot of sense. Only thing I can think
of is that
> > > there must be some extra prefetching going on in the domU case.
It
> > still
> > > doesn''t explain why the dom0 result is so much worse
than native.
> > >
> > > It might be worth repeating with both native and dom0 boot with
> > > maxcpus=1.
> > >
> > > Are you using near-identical kernels in both cases? Same
> > drivers, same
> > > part of the disk for the tests, etc?
> > >
> > > How are you doing the measurement? A timed
''dd''?
> > >
> > > Ian
> > >
> > >
> > > > 256K Sequential Write
> > > > Linux Native: 668.9MB/s
> > > > Xen Domain0: 708.7MB/s
> > > > Xen DomainU: 373.5MB/s
> > > >
> > > > Just two questions:
> > > >
> > > > It seems para-virtualized DomU outperform Dom0 in terms of
> > sequential
> > > read
> > > > and is very to Linux native performance. However, DomU does
show
> > poor
> > > (only
> > > > 50%) sequential write performance compared with Linux native
and
> > Dom0.
> > > >
> > > > Could you explain some reason behind this?
> > > >
> > > > Thanks,
> > > >
> > > > Liang
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > > > To: "John Byrne" <john.l.byrne@hp.com>
> > > > Cc: "xen-devel"
<xen-devel@lists.xensource.com>;
> > "Emmanuel Ackaouy"
> > > > <ack@xensource.com>
> > > > Sent: Tuesday, November 07, 2006 10:20 AM
> > > > Subject: RE: [Xen-devel] Direct I/O to domU seeing a 30%
> > performance
> > > hit
> > > >
> > > >
> > > > > Both dom0 and the domU are SLES 10, so I don''t
know why
> > the "idle"
> > > > > performance of the two should be different. The obvious
> > asymmetry
> > is
> > > > the
> > > > > disk. Since the disk isn''t direct, any disk
I/O by the
> > domU would
> > > > > certainly impact dom0, but I don''t think there
should
> > be much, if
> > > any.
> > > > I
> > > > > did run a dom0 test with the domU started, but idle and
> > there was
> > no
> > > > > real change to dom0''s numbers.
> > > > >
> > > > > What''s the best way to gather information
about what is going on
> > > with
> > > > > the domains without perturbing them? (Or, at least,
perturbing
> > > > everyone
> > > > > equally.)
> > > > >
> > > > > As to the test, I am running netperf 2.4.1 on an
outside machine
> > to
> > > > the
> > > > > dom0 and the domU. (So the doms are running the
netserver
> > portion.)
> > > I
> > > > > was originally running it in the doms to the outside
> > machine, but
> > > when
> > > > > the bad numbers showed up I moved it to the outside
machine
> > because
> > > I
> > > > > wondered if the bad numbers were due to something
> > happening to the
> > > > > system time in domU. The numbers is the
"outside" test to domU
> > look
> > > > worse.
> > > >
> > > >
> > > > It might be worth checking that there''s no
interrupt sharing
> > > happening.
> > > > While running the test against the domU, see how much CPU
> > dom0 burns
> > > in
> > > > the same period using ''xm vcpu-list''.
> > > >
> > > > To keep things simple, have dom0 and domU as uniprocessor
guests.
> > > >
> > > > Ian
> > > >
> > > >
> > > > > Ian Pratt wrote:
> > > > > >
> > > > > >> There have been a couple of network receive
throughput
> > > > > >> performance regressions to domUs over time
that were
> > > > > >> subsequently fixed. I think one may have crept
in to 3.0.3.
> > > > > >
> > > > > > The report was (I believe) with a NIC directly
assigned to the
> > > domU,
> > > > so
> > > > > > not using netfront/back at all.
> > > > > >
> > > > > > John: please can you give more details on your
config.
> > > > > >
> > > > > > Ian
> > > > > >
> > > > > >> Are you seeing any dropped packets on the vif
associated with
> > > > > >> your domU in your dom0? If so, propagating
changeset
> > > > > >> 11861 from unstable may help:
> > > > > >>
> > > > > >> changeset:   11861:637eace6d5c6
> > > > > >> user:        kfraser@localhost.localdomain
> > > > > >> date:        Mon Oct 23 11:20:37 2006 +0100
> > > > > >> summary:     [NET] back: Fix packet queuing so
that packets
> > > > > >> are drained if the
> > > > > >>
> > > > > >>
> > > > > >> In the past, we also had receive throughput
issues to domUs
> > > > > >> that were due to socket buffer size logic but
those were
> > > > > >> fixed a while ago.
> > > > > >>
> > > > > >> Can you send netstat -i output from dom0?
> > > > > >>
> > > > > >> Emmanuel.
> > > > > >>
> > > > > >>
> > > > > >> On Mon, Nov 06, 2006 at 09:55:17PM -0800, John
Byrne wrote:
> > > > > >>> I was asked to test direct I/O to a PV
domU. Since, I had a
> > > system
> > > > > >>> with two NICs, I gave one to a domU and
one dom0. (Each is
> > > > > >> running the
> > > > > >>> same
> > > > > >>> kernel: xen 3.0.3 x86_64.)
> > > > > >>>
> > > > > >>> I''m running netperf from an
outside system to the domU and
> > > > > >> dom0 and I
> > > > > >>> am seeing 30% less throughput for the domU
vs dom0.
> > > > > >>>
> > > > > >>> Is this to be expected? If so, why? If
not, does anyone
> > > > > >> have a guess
> > > > > >>> as to what I might be doing wrong or what
the issue
> > might be?
> > > > > >>>
> > > > > >>> Thanks,
> > > > > >>>
> > > > > >>> John Byrne
> > > > > >>
_______________________________________________
> > > > > >> 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
> > > > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > 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
>
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

Liang Yang

2006-Nov-07 18:55 UTC

head link

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

Hi Ian,

I already tested the performance for four I/O schedulers: noop, deadline, 
Anticipatory and CFQ. There is performance impact with I/O schedulers, 
however
the performance difference between those four I/O schedulers are all less 
than 10%.

I find Anticipaotry could be the best choice. So I used Anticipatory as the 
Linux I/O scheduler for all my testing Linux native, Xen Domain0 and DomainU 
(this change does not show in the config files).

Liang

----- Original Message ----- 
From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
To: "Liang Yang" <multisyncfe991@hotmail.com>; "John
Byrne"
<john.l.byrne@hp.com>
Cc: "xen-devel" <xen-devel@lists.xensource.com>; "Emmanuel
Ackaouy"
<ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
Sent: Tuesday, November 07, 2006 11:45 AM
Subject: RE: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: 
[Xen-devel] Direct I/O to domU seeing a 30% performance hit

> Attached is the diff of the two kernel configs.
There are a *lot* of differences between those kernel configs. A cursory
glance spots such gems as:

< CONFIG_DEFAULT_IOSCHED="cfq"
---> CONFIG_DEFAULT_IOSCHED="anticipatory"
All bets are off.

Ian

> ----- Original Message -----
> From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> To: "Liang Yang" <yangliang_mr@hotmail.com>; "John
Byrne"
> <john.l.byrne@hp.com>
> Cc: "xen-devel" <xen-devel@lists.xensource.com>;
"Emmanuel Ackaouy"
> <ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
> Sent: Tuesday, November 07, 2006 11:15 AM
> Subject: RE: Performance data of Linux native vs. Xen Dom0
> and Xen DomU. Re:
> [Xen-devel] Direct I/O to domU seeing a 30% performance hit
>
>
> > I already set dom0_max_vcpus=1 for domain0 when I was doing testing.
> Also,
> > Linux native kernel and domU kernel are all compiled as
> Uni-Processor
> > mode.All the testing for Linux native, domain0 and domainU
> are exactly
> the
> > same. All used Linux kernel 2.6.16.29.
>
> Please could you post a ''diff'' of the two kernel configs.
>
> It might be worth diff''ing the boot messages in both cases too.
>
> Thanks,
> Ian
>
>
> > Regards,
> >
> > Liang
> >
> > ----- Original Message -----
> > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > To: "Liang Yang" <multisyncfe991@hotmail.com>;
"John Byrne"
> > <john.l.byrne@hp.com>
> > Cc: "xen-devel" <xen-devel@lists.xensource.com>;
"Emmanuel Ackaouy"
> > <ack@xensource.com>; <ian.pratt@cl.cam.ac.uk>
> > Sent: Tuesday, November 07, 2006 11:06 AM
> > Subject: RE: Performance data of Linux native vs. Xen Dom0 and Xen
> DomU.
> > Re:
> > [Xen-devel] Direct I/O to domU seeing a 30% performance hit
> >
> >
> > > I''m also doing some performance analysis about Linux
native, dom0
> and
> > domU
> > > (para-virtualized). Here are some brief comparison for 256K
> sequential
> > > read/write. The testing is done using for JBOD based on 8
> Maxtor SAS
> > Atlas
> > > 2
> > > 15K drives with LSI SAS HBA.
> > >
> > > 256K Sequential Read
> > > Linux Native: 559.6MB/s
> > > Xen Domain0: 423.3MB/s
> > > Xen DomainU: 555.9MB/s
> >
> > This doesn''t make a lot of sense. Only thing I can think of
is that
> > there must be some extra prefetching going on in the domU case. It
> still
> > doesn''t explain why the dom0 result is so much worse than
native.
> >
> > It might be worth repeating with both native and dom0 boot with
> > maxcpus=1.
> >
> > Are you using near-identical kernels in both cases? Same
> drivers, same
> > part of the disk for the tests, etc?
> >
> > How are you doing the measurement? A timed ''dd''?
> >
> > Ian
> >
> >
> > > 256K Sequential Write
> > > Linux Native: 668.9MB/s
> > > Xen Domain0: 708.7MB/s
> > > Xen DomainU: 373.5MB/s
> > >
> > > Just two questions:
> > >
> > > It seems para-virtualized DomU outperform Dom0 in terms of
> sequential
> > read
> > > and is very to Linux native performance. However, DomU does show
> poor
> > (only
> > > 50%) sequential write performance compared with Linux native and
> Dom0.
> > >
> > > Could you explain some reason behind this?
> > >
> > > Thanks,
> > >
> > > Liang
> > >
> > >
> > > ----- Original Message -----
> > > From: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>
> > > To: "John Byrne" <john.l.byrne@hp.com>
> > > Cc: "xen-devel" <xen-devel@lists.xensource.com>;
> "Emmanuel Ackaouy"
> > > <ack@xensource.com>
> > > Sent: Tuesday, November 07, 2006 10:20 AM
> > > Subject: RE: [Xen-devel] Direct I/O to domU seeing a 30%
> performance
> > hit
> > >
> > >
> > > > Both dom0 and the domU are SLES 10, so I don''t know
why
> the "idle"
> > > > performance of the two should be different. The obvious
> asymmetry
> is
> > > the
> > > > disk. Since the disk isn''t direct, any disk I/O by
the
> domU would
> > > > certainly impact dom0, but I don''t think there
should
> be much, if
> > any.
> > > I
> > > > did run a dom0 test with the domU started, but idle and
> there was
> no
> > > > real change to dom0''s numbers.
> > > >
> > > > What''s the best way to gather information about
what is going on
> > with
> > > > the domains without perturbing them? (Or, at least,
perturbing
> > > everyone
> > > > equally.)
> > > >
> > > > As to the test, I am running netperf 2.4.1 on an outside
machine
> to
> > > the
> > > > dom0 and the domU. (So the doms are running the netserver
> portion.)
> > I
> > > > was originally running it in the doms to the outside
> machine, but
> > when
> > > > the bad numbers showed up I moved it to the outside machine
> because
> > I
> > > > wondered if the bad numbers were due to something
> happening to the
> > > > system time in domU. The numbers is the "outside"
test to domU
> look
> > > worse.
> > >
> > >
> > > It might be worth checking that there''s no interrupt
sharing
> > happening.
> > > While running the test against the domU, see how much CPU
> dom0 burns
> > in
> > > the same period using ''xm vcpu-list''.
> > >
> > > To keep things simple, have dom0 and domU as uniprocessor guests.
> > >
> > > Ian
> > >
> > >
> > > > Ian Pratt wrote:
> > > > >
> > > > >> There have been a couple of network receive
throughput
> > > > >> performance regressions to domUs over time that
were
> > > > >> subsequently fixed. I think one may have crept in
to 3.0.3.
> > > > >
> > > > > The report was (I believe) with a NIC directly assigned
to the
> > domU,
> > > so
> > > > > not using netfront/back at all.
> > > > >
> > > > > John: please can you give more details on your config.
> > > > >
> > > > > Ian
> > > > >
> > > > >> Are you seeing any dropped packets on the vif
associated with
> > > > >> your domU in your dom0? If so, propagating
changeset
> > > > >> 11861 from unstable may help:
> > > > >>
> > > > >> changeset:   11861:637eace6d5c6
> > > > >> user:        kfraser@localhost.localdomain
> > > > >> date:        Mon Oct 23 11:20:37 2006 +0100
> > > > >> summary:     [NET] back: Fix packet queuing so that
packets
> > > > >> are drained if the
> > > > >>
> > > > >>
> > > > >> In the past, we also had receive throughput issues
to domUs
> > > > >> that were due to socket buffer size logic but those
were
> > > > >> fixed a while ago.
> > > > >>
> > > > >> Can you send netstat -i output from dom0?
> > > > >>
> > > > >> Emmanuel.
> > > > >>
> > > > >>
> > > > >> On Mon, Nov 06, 2006 at 09:55:17PM -0800, John
Byrne wrote:
> > > > >>> I was asked to test direct I/O to a PV domU.
Since, I had a
> > system
> > > > >>> with two NICs, I gave one to a domU and one
dom0. (Each is
> > > > >> running the
> > > > >>> same
> > > > >>> kernel: xen 3.0.3 x86_64.)
> > > > >>>
> > > > >>> I''m running netperf from an outside
system to the domU and
> > > > >> dom0 and I
> > > > >>> am seeing 30% less throughput for the domU vs
dom0.
> > > > >>>
> > > > >>> Is this to be expected? If so, why? If not,
does anyone
> > > > >> have a guess
> > > > >>> as to what I might be doing wrong or what the
issue
> might be?
> > > > >>>
> > > > >>> Thanks,
> > > > >>>
> > > > >>> John Byrne
> > > > >> _______________________________________________
> > > > >> 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
> > > > >
> > >
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@lists.xensource.com
> > > http://lists.xensource.com/xen-devel
> >
>
>

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Liang Yang

2006-Nov-09 00:43 UTC

head link

[Xen-devel] Xen DomU (vt-x) reports CPU utilization ZERO!!!

Hello,

It seems Linux kernel under Xen DomainU (full-virtualized mode) reports the 
CPU utilization incorrectly. All CPU utilization data reported under 
/proc/stat are 0.

Anyone has any idea about how to solve this issue?

Liang 


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Ulrich Windl

2006-Nov-09 07:47 UTC

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Re: [Xen-users] Xen DomU (vt-x) reports CPU utilization ZERO!!!

On 8 Nov 2006 at 17:43, Liang Yang wrote:
> Hello,
> 
> It seems Linux kernel under Xen DomainU (full-virtualized mode) reports the
> CPU utilization incorrectly. All CPU utilization data reported under 
> /proc/stat are 0.
> 
> Anyone has any idea about how to solve this issue?
Hi!

I think(!) that the CPU usage is lower that usual, because the scheduling
overhead
and real I/O stuff is don in Dom0 invisible to DomUs. While my load is really 
quite low now, it''s not exactly zero (in DomU):

top - 08:46:08 up 6 days, 43 min,  1 user,  load average: 0.00, 0.00, 0.00
Tasks:  73 total,   2 running,  71 sleeping,   0 stopped,   0 zombie
Cpu0  :  0.1%us,  0.0%sy,  0.0%ni, 99.8%id,  0.1%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu1  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st

See, I have a little CPU usage ;-)

Regards,
Ulrich


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Christopher G. Stach II

2006-Nov-13 15:49 UTC

head link

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

George Dunlap wrote:> One of the strange things, though, is that the difference should be so
> big between domU and dom0, which are using the exact same same kernel
> (correct me if I''m wrong).
> 
> I''m not familiar with the I/O scheduling.  Is it possible that the
I/O
> scheduling inside the domU is interacting poorly with the I/O
> scheduling in dom0?  That''s one hypothesis for why domU writes are
> slower than dom0 writes; but that doesn''t seem to explain why domU
> reads would be *faster* than dom0 reads.
> 
> -George
Correct me if I''m wrong, but wouldn''t a file-backed block
device for the
domU be reading from memory if it''s cached in the dom0?  That would be
a
bit faster.

Also, in the past it seemed the domU schedulers were ignored and were
implicitly noop, relying on the dom0''s scheduler (which did all of the
real I/O.)  Has this changed?

-- 
Christopher G. Stach II

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Liang Yang

2006-Nov-13 16:18 UTC

head link

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

Hi,

I did not use any file backed block devices. To get the real disk I/O 
performance for guest domains, all the guest domain OS are installed on the 
separate logic volumes (each guest domain is installed on independent hard 
drives).

I tried to change the I/O scheduler for both guest domain (noop is the 
default) and domain0 to anticipatory, but the results are the same as I 
collected before.

Regards,

Liang

----- Original Message ----- 
From: "Christopher G. Stach II" <cgs@ldsys.net>
To: "George Dunlap" <gdunlap@xensource.com>
Cc: "Ian Pratt" <m+Ian.Pratt@cl.cam.ac.uk>; "Emmanuel
Ackaouy"
<ack@xensource.com>; "Liang Yang"
<multisyncfe991@hotmail.com>; "xen-devel"
<xen-devel@lists.xensource.com>; "John Byrne"
<john.l.byrne@hp.com>
Sent: Monday, November 13, 2006 8:49 AM
Subject: Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: 
[Xen-devel] Direct I/O to domU seeing a 30% performance hit

> George Dunlap wrote:
>> One of the strange things, though, is that the difference should be so
>> big between domU and dom0, which are using the exact same same kernel
>> (correct me if I''m wrong).
>>
>> I''m not familiar with the I/O scheduling.  Is it possible that
the I/O
>> scheduling inside the domU is interacting poorly with the I/O
>> scheduling in dom0?  That''s one hypothesis for why domU writes
are
>> slower than dom0 writes; but that doesn''t seem to explain why
domU
>> reads would be *faster* than dom0 reads.
>>
>> -George
>
> Correct me if I''m wrong, but wouldn''t a file-backed block
device for the
> domU be reading from memory if it''s cached in the dom0?  That
would be a
> bit faster.
>
> Also, in the past it seemed the domU schedulers were ignored and were
> implicitly noop, relying on the dom0''s scheduler (which did all of
the
> real I/O.)  Has this changed?
>
> -- 
> Christopher G. Stach II
> 

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Xen devel - Nov 2006 - RE: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: Direct I/O to domU seeing a 30% performance hit

RE: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

[Xen-devel] Xen DomU (vt-x) reports CPU utilization ZERO!!!

Re: [Xen-users] Xen DomU (vt-x) reports CPU utilization ZERO!!!

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit

Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: [Xen-devel] Direct I/O to domU seeing a 30% performance hit