Re: [PATCH 0/9] Per-cgroup /proc/stat

[Peter Zijlstra]

On Wed, 2011-09-14 at 13:23 -0700, Andi Kleen wrote:
> Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> writes:
> >
> > Guys we should seriously trim back a lot of that code, not grow ever
> > more and more. The sad fact is that if you build a kernel with
> > cpu-cgroup support the context switch cost is more than double that of a
> > kernel without, and then you haven't even started creating cgroups yet.
> 
> That sounds indeed quite bad. Is it known why it is so costly?

Mostly because all data structures grow and all code paths grow, some by
quite a bit, its spread all over the place, lots of little cuts etc..

pjt and I tried trimming some of the code paths with static_branch() but
didn't really get anywhere.. need to get back to looking at this stuff
sometime soon.
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