linux-kernel - Re: [RESEND][PATCH] mm: vmstats: tlb flush counters

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Date:	Thu, 18 Jul 2013 13:51:57 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux-mm@...ck.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RESEND][PATCH] mm: vmstats: tlb flush counters

On Wed, 17 Jul 2013 09:21:00 +0200 Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Dave Hansen <dave@...1.net> wrote:
> 
> > I was investigating some TLB flush scaling issues and realized
> > that we do not have any good methods for figuring out how many
> > TLB flushes we are doing.
> > 
> > It would be nice to be able to do these in generic code, but the
> > arch-independent calls don't explicitly specify whether we
> > actually need to do remote flushes or not.  In the end, we really
> > need to know if we actually _did_ global vs. local invalidations,
> > so that leaves us with few options other than to muck with the
> > counters from arch-specific code.

Spose so, if you really think it's worth it.  It's all downside for
uniprocessor machines.  And for architectures which don't implement the
counters, of course.

> > --- linux.git/include/linux/vm_event_item.h~tlb-vmstats	2013-07-16 16:41:56.478280438 -0700
> > +++ linux.git-davehans/include/linux/vm_event_item.h	2013-07-16 16:41:56.483280658 -0700
> > @@ -70,6 +70,11 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS
> >  		THP_ZERO_PAGE_ALLOC,
> >  		THP_ZERO_PAGE_ALLOC_FAILED,
> >  #endif
> >
> > +		NR_TLB_REMOTE_FLUSH,	/* cpu tried to flush others' tlbs */
> > +		NR_TLB_REMOTE_FLUSH_RECEIVED,/* cpu received ipi for flush */
> > +		NR_TLB_LOCAL_FLUSH_ALL,
> > +		NR_TLB_LOCAL_FLUSH_ONE,
> > +		NR_TLB_LOCAL_FLUSH_ONE_KERNEL,
> 
> Please fix the vertical alignment of comments.

I looked - this isn't practical.

It would be nice to actually document these things though.  We don't
*have* to squeeze the comment into the RHS.

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