Re: Linux 3.19-rc3

Kyle McMartin
2015-01-10T15:23:39Z

On Sat, Jan 10, 2015 at 04:29:39AM +0100, Laszlo Ersek wrote:
> I've bisected this issue to
>

Awesome, this was on my list of list of suspicious commits to check
before my ARM64 box decided not to come back from reboot on Friday. :)

Thanks for bisecting!

cheers,
--Kyle

> > f045bbb9fa1bf6f507ad4de12d4e3471d8f672f1 is the first bad commit
> > commit f045bbb9fa1bf6f507ad4de12d4e3471d8f672f1
> > Author: Linus Torvalds <torvalds@linux-foundation.org>
> > Date: Wed Dec 17 11:59:04 2014 -0800
> >
> > mmu_gather: fix over-eager tlb_flush_mmu_free() calling
> >
> > Dave Hansen reports that commit fb7332a9fedf ("mmu_gather: move minimal
> > range calculations into generic code") caused a performance problem:
> >
> > "tlb_finish_mmu() goes up about 9x in the profiles (~0.4%->3.6%) and
> > tlb_flush_mmu_free() takes about 3.1% of CPU time with the patch
> > applied, but does not show up at all on the commit before"
> >
> > and the reason is that Will moved the test for whether we need to flush
> > from tlb_flush_mmu() into tlb_flush_mmu_tlbonly(). But that meant that
> > tlb_flush_mmu_free() basically lost that check.
> >
> > Move it back into tlb_flush_mmu() where it belongs, so that it covers
> > both tlb_flush_mmu_tlbonly() _and_ tlb_flush_mmu_free().
> >
> > Reported-and-tested-by: Dave Hansen <dave@sr71.net>
> > Acked-by: Will Deacon <will.deacon@arm.com>
> > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> >