Re: REGRESSION: Performance regressions from switchinganon_vma->lock to mutex

[Tim Chen]

On Wed, 2011-06-15 at 13:57 -0700, Andi Kleen wrote:
> >       7.44%        exim  [kernel.kallsyms]              [k] format_decode
> >                    |
> >                    --- format_decod
> 
> 
> This is a glibc issue. exim calls libdb and libdb asks sysconf for the 
> number of CPUs to tune
> its locking, and glibc reads /proc/stat.  And /proc/stat is incredible slow.
> 
> I would blame glibc, but in this case it's really the kernel to blame 
> for not providing proper
> interface.
> 
> This was my motivation for the sysconf() syscall I submitted some time ago.
> https://lkml.org/lkml/2011/5/13/455
> 
> Anyways a quick workaround is to use this LD_PRELOAD: 
> http://halobates.de/smallsrc/sysconf.c
> But it's not 100% equivalent.
> 

Thanks to Andi for providing the info.  We've used this workaround in
our testing so it will not mask true kernel scaling bottlenecks.

Tim

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