2 x quad-core system is slower that 2 x dual core on FreeBSD

[Max Laier]

On Tuesday 20 November 2007, Kris Kennaway wrote:
> Kris Kennaway wrote:
> > Kris Kennaway wrote:
> >> In the meantime there is unfortunately not a lot that can be done,
> >> AFAICT.  There is one hack that I will send you later but it is not
> >> likely to help much.  I will also think about how to track down the
> >> cause of the contention further (the profiling trace only shows that
> >> it comes mostly from vget/vput but doesn't show where these are
> >> called from).
> >
> > Actually this patch might help.  It doesn't replace lockmgr but it
> > does fix a silly thundering herd behaviour.  It probably needs some
> > adjustment to get it to apply cleanly (it is about 7 months old), and
> > I apparently stopped using it because I ran into deadlocks.  It might
> > be stable enough to at least see how much it helps.
> >
> > Set the vfs.lookup_shared=1 sysctl to enable the other half of the
> > patch.
> >
> > Kris
>
> Try this one instead, it applies to HEAD.  You'll need to manually
> enter the paths though because of how p4 mangles diffs.

I rolled a tiny, simple, possibly braindamaged benchmark (but then again 
php code tends to be braindamaged): test.php includes 1000 different, 
essential empty files and is strated over and over from a shell script 
which counts the runs completed within 60seconds.  1-8,128 scripts are 
started in parallel.

On a 2x dual Opteron running amd64 I get:

stock RELENG_7 w/o patch ULE:
jobs  sum runs   gain
  1       617    1
  2       784    1.27
  3       939    1.52
  4      1015    1.65
  5       658    1.07
  6       642    1.04
  7       666    1.08
  8       696    1.13
128       726    1.18

RELENG_7 patched ULE vfs.lookup_shared=1:
jobs  sum runs   gain
  1       637    1
  2       784    1.23
  3       973    1.53
  4      1104    1.73
  5       708    1.11
  6       733    1.15
  7       776    1.22
  8       840    1.32
128       936    1.47

So there is still a lot of room for improvement here.  I'll rebuild with 
lock profiling tomorrow and see what I can gather.  Anything you'd like 
to see in particular?

-- 
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