lkml.org 
[lkml]   [2001]   [Oct]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [Bench] New benchmark showing fileserver problem in 2.4.12
On Oct 17, 2001  23:06 +1000, Robert Cohen wrote:
> Factor 1: the performance problems only occur when you are rewriting an
> existing file in place. That is writing to an existing file which is
> opened without O_TRUNC. Equivalently, if you have written a file and
> then seek'ed back to the beginning and started writing again.
>
> Evidence: in the report I posted yesterday, the test I was using
> involved 5 clients rewriting 30 Meg files on a 128 Meg machine. The
> symptom was that after about 10 seconds, the throughput as shown by
> vmstat "bo" drops sharply and we start getting reads occuring as shown
> by the "bi" figure.

Just a guess - if you are getting reads that are about the same as writes,
then it would indicate that the code is doing "read-modify-write" for the
existing file data rather than just "write". This would be caused by not
writing only full-sized aligned blocks to the files.

As to why this is happening only over the network - it may be that you are
are unable to send an even multiple of the blocksize over the network (MTU)
and this is causing fragmented writes. Try using a smaller block size like
4k or so to see if it makes a difference.

Another possibility is that with 8k chunks you are needing order-1
allocations to receive the data and this is causing a lot of searching for
buffers to free.

Cheers, Andreas
--
Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto,
\ would they cancel out, leaving him still hungry?"
http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:08    [W:0.121 / U:0.756 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site