Re: SMP performance degradation with sysbench

[Nick Piggin]

Eric Dumazet wrote:
> On Tuesday 13 March 2007 12:12, Nick Piggin wrote:
>
> > I guess googlemalloc (tcmalloc?) isn't suitable for a general purpose
> > glibc allocator. But I wonder if there are other improvements that glibc
> > can do here?
>
>
> I cooked a patch some time ago to speedup threaded apps and got no feedback.

Well that doesn't help in this case. I tested and the mmap_sem contention
is not an issue.

> http://lkml.org/lkml/2006/8/9/26
>
> Maybe we have to wait for 32 core cpu before thinking of cache line 
> bouncings...

The idea is a good one, and I was half way through implementing similar
myself at one point (some java apps hit this badly).

It is just horribly sad that futexes are supposed to implement a
_scalable_ thread synchronisation mechanism, whilst fundamentally
relying on an mm-wide lock to operate.

I don't like your interface, but then again, the futex interface isn't
exactly pretty anyway.

You should resubmit the patch, and get the glibc guys to use it.

--
SUSE Labs, Novell Inc.
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