Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex

Tim Chen
2011-06-15T21:11:42Z

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