Messages in this thread | | | Date | Fri, 18 Sep 2009 09:12:17 +0200 | From | Andi Kleen <> | Subject | Re: aim7 scalability issue on 4 socket machine |
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On Fri, Sep 18, 2009 at 07:53:58AM +0100, Hugh Dickins wrote: > On Thu, 17 Sep 2009, Andrew Morton wrote: > > On Fri, 18 Sep 2009 10:02:19 +0800 "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote: > > > > > > > > So, Yanmin, please retest with http://lkml.org/lkml/2009/9/13/25 > > > > and let us know if that works as well for you - thanks. > > > I tested Lee's patch and it does fix the issue. > > Thanks for checking and reporting back, Yanmin. > > > > > Do we think we should cook up something for -stable? > > Gosh, I laughed at Lee (sorry!) for suggesting it for -stable: > is stable really for getting a better number out of a benchmark?
When your system is large enough scalability problems (e.g. lock contention) can be a serious bug. i.e. when your workload is 150% slower than expected that can well be a show stopper.
Admittedly the workload in this case was a benchmark, but it's not that far fetched to expect the same problem in a real application.
We had a similar problem with the accounting lock some time ago, I think that patch also went in.
So yes I think simple non intrusive fixes for serious scalability problems should be stable candidates.
> > Either this is a regression or the workload is particularly obscure. > > I've not cross-checked descriptions, but assume Lee was actually > testing on exactly the same kind of upcoming Nehalem as Yanmin, and > that machine happens to have characteristics which show up badly here.
AFAIK Lee usually tests on large IA64 boxes.
> > aim7 is sufficiently non-obscure to make me wonder what's happened here? > > Not a regression, just the onward march of new hardware, I think. > Could easily be other such things in other places with other tests.
Yes, it's just a much larger machine, so old hidden scalability sins now appear.
-Andi
-- ak@linux.intel.com -- Speaking for myself only.
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