I mentioned a similar problem about a month ago. Jens Axboe provided
a patch which re-worked the elevator code and restored performance to
2.2 levels. I think you'll be able to find his patches in the
"people" directory.
Michal Ostrowski
mostrows@styx.uwaterloo.ca
dvdan23@hotmail.com ("Daniel Summer") writes:
> Hello kernel hackers. I have been concerned about a serious performance
> issue affecting bonnie disk benchmark results that has persisted throughout
> 2.3 and 2.4 development. This issue has been brought up many times on this
> list and there doesn't seem to be a consensus as to what the origin of the
> problem is. Some have pointed to the elevator code, some to the VM
> subsystem, some to the block interfaces.
>
> Joel Jacobsen of 3ware pointed out that these poor benchmark results may
> arise from problems with the buffer cache (see his comments below). I went
> ahead and ran some benchmarks with different quantities of RAM across 2.2
> and 2.4 to see if I could shed some light on this.
>
> I found that bumping the RAM from 512megs to a gig gives a huge performance
> boost under 2.4 and makes little to no impact under 2.2.16. Even with a gig
> of RAM though, 2.4 still performs much worse than 2.2 at sequential reads.
>
> So what does this mean? does anyone else agree that the buffer cache may be
> where this problem is coming from?
>
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