Re: disk performance still wrecked in 2.4!

[Michal Ostrowski]

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
[e-mail]

[e-mail] ("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?
>