On Tue, Sep 02, 2014 at 05:20:55PM -0700, Linus Torvalds wrote:
> On Tue, Sep 2, 2014 at 5:10 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> >
> > That looks like a partial profile, where did the page allocator, page
> > zeroing etc. go? Because the distribution among these listed symbols
> > doesn't seem all that crazy:
>
> Please argue this *after* the commit has been reverted. You guys can
> try to make the memcontrol batching actually work and scale later.
> It's not appropriate to argue against major regressions when reported
> and bisected by users.
I'll send a clean revert later.
> Showing the spinlock at the top of the profile is very much crazy
> (apparently taking 68% of all cpu time), when it's all useless
> make-believe work. I don't understand why you wouldn't call that
> crazy.
If you limit perf to a subset of symbols, it will show a relative
distribution between them, i.e: perf top --symbols kfree,memset during
some disk access:
PerfTop: 1292 irqs/sec kernel:84.4% exact: 0.0% [4000Hz cycles], (all, 4 CPUs)
-------------------------------------------------------------------------------
56.23% [kernel] [k] kfree
41.86% [kernel] [k] memset
1.91% libc-2.19.so [.] memset
kfree isn't eating 56% of "all cpu time" here, and it wasn't clear to
me whether Dave filtered symbols from only memcontrol.o, memory.o, and
mmap.o in a similar way. I'm not arguing against the regression, I'm
just trying to make sense of the numbers from the *patched* kernel.
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