Re: 2.4.8-pre1 and dbench -20% throughput

From: Daniel Phillips (
Date: Fri Jul 27 2001 - 17:34:05 EST

On Friday 27 July 2001 23:08, Roger Larsson wrote:
> Hi all,
> I have done some throughput testing again.
> Streaming write, copy, read, diff are almost identical to earlier 2.4
> kernels. (Note: 2.4.0 was clearly better when reading from two files
> - i.e. diff - 15.4 MB/s v. around 11 MB/s with later kenels - can be
> a result of disk layout too...)
> But "dbench 32" (on my 256 MB box) results has are the most
> interesting:
> 2.4.0 gave 33 MB/s
> 2.4.8-pre1 gives 26.1 MB/s (-21%)
> Do we now throw away pages that would be reused?
> [I have also verified that mmap002 still works as expected]

Could you run that test again with /usr/bin/time (the GNU time
function) so we can see what kind of swapping it's doing?

The use-once approach depends on having a fairly stable inactive_dirty
+ inactive_clean queue size, to give use-often pages a fair chance to
be rescued. To see how the sizes of the queues are changing, use
Shift-ScrollLock on your text console.

To tell the truth, I don't have a deep understanding of how dbench
works. I should read the code now and see if I can learn more about it
:-/ I have noticed that it tends to be highly variable in performance,
sometimes showing variation of a few 10's of percents from run to run.
This variation seems to depend a lot on scheduling. Do you see "*"'s
evenly spaced throughout the tracing output, or do you see most of them
bunched up near the end?

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This archive was generated by hypermail 2b29 : Tue Jul 31 2001 - 21:00:35 EST