Re: page fault scalability patch v3: use cmpxchg, make rss atomic

Christoph Lameter
2004-08-24T14:48:33Z

On Tue, 24 Aug 2004, Matthew Wilcox wrote:

> On Mon, Aug 23, 2004 at 10:49:31PM -0700, Christoph Lameter wrote:
> > Unpatched:
> > Gb Rep Threads User System Wall flt/cpu/s fault/wsec
> > 4 3 1 0.157s 11.197s 11.035s 69261.721 69239.940
> > 4 3 2 0.145s 11.445s 6.079s 67849.528 115681.409
> > 4 3 4 0.182s 13.894s 4.027s 55865.834 184108.856
> > 4 3 8 0.196s 24.874s 4.025s 31369.039 184790.767
> >
> > With page fault scalability patch:
> > Gb Rep Threads User System Wall flt/cpu/s fault/wsec
> > 4 3 1 0.176s 11.323s 11.050s 68385.368 68345.055
> > 4 3 2 0.174s 10.716s 5.096s 72205.329 131848.322
> > 4 3 4 0.170s 10.694s 3.040s 72380.552 231128.569
> > 4 3 8 0.177s 14.717s 2.064s 52796.567 297380.041
>
> What kind of variance are you seeing with this benchmark? I'm suspicious
> that your 2 thread case is faster than your single thread case.

What is so suspicious about it? Two CPUs can do the job faster than a
single one. Thats the way it should be and the point of these
patches is to reduce locking so that this can happen in a more efficient
way.

There are some variances in these tests especially if one uses low memory
settings such as 1GB 2GB and to some extend also at 4GB. 16 GB gives quite
stable results but the machine I had available for this only had 8 GB. See
my earlier posts on the subject for other test results.