Ext3 users - Feb 2002 - ext3 blocks other with large writes

Hi there,

First of all thanks for all the ext3 development! I run it on my laptop
and it has saved me many times from lengthy fscks :-)

However, I have observed that whenever something is doing a lot of
writing to an ext3 filesystem other processes that involves I/O on the
same disk are blocked for long times (often in the 10-30 secs range).
For example, if I cp a 1.5 Gb file from one ext3 partition to another
ext3 partition and I try to do ls on some dir, the ls usually blocks
between 10 and 30 secs before giving a response (the CPU usage is no
more than 10% during this). However if the destination partition for the
cp is mounted as ext2, the ls command responds almost immediately.

Is there some setting that can be tuned to avoid such a behaviour?

I'm currently running RedHat 7.2, kernel 2.4.9-21

hdparm /dev/hda:

/dev/hda:
 multcount    = 16 (on)
 I/O support  =  1 (32-bit)
 unmaskirq    =  1 (on)
 using_dma    =  1 (on)
 keepsettings =  0 (off)
 nowerr       =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 2343/240/63, sectors = 35433216, start = 0

And from dmesg:

hda: IBM-DARA-218000, ATA DISK drive
hda: 35433216 sectors (18142 MB) w/418KiB Cache, CHS=2343/240/63,
UDMA(33)


Thanks for any help,

Diego
-- 
-------------------------------------------------------
Diego Santa Cruz
PhD. student
Publications available at http://ltswww.epfl.ch/~dsanta
Signal Processing Laboratory (LTS)
Swiss Federal Institute of Technology (EPFL)
EPFL - DE - LTS, CH-1015 Lausanne, Switzerland
E-mail:     Diego.SantaCruz@epfl.ch
Phone:      +41 - 21 - 693 26 57
Fax:        +41 - 21 - 693 76 00
-------------------------------------------------------

On Feb 28, 2002  13:35 +0100, Diego SANTA CRUZ wrote:
> However, I have observed that whenever something is doing a lot of
> writing to an ext3 filesystem other processes that involves I/O on the
> same disk are blocked for long times (often in the 10-30 secs range).
> For example, if I cp a 1.5 Gb file from one ext3 partition to another
> ext3 partition and I try to do ls on some dir, the ls usually blocks
> between 10 and 30 secs before giving a response (the CPU usage is no
> more than 10% during this). However if the destination partition for the
> cp is mounted as ext2, the ls command responds almost immediately.
I don't think this is so much an ext3 problem as an elevator starvation
problem.  You should try using Andrew's elevator starvation fix (sorry,
don't know URL), which allows read requests to be put earlier in the
queue so you don't get such long waits.

Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/