linux-kernel - Re: [PATCH 0/3] TLB flush multiple pages per IPI v5

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Date:	Sun, 21 Jun 2015 23:22:31 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Dave Hansen <dave.hansen@...el.com>, Ingo Molnar <mingo@...nel.org>
Cc:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	H Peter Anvin <hpa@...or.com>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/3] TLB flush multiple pages per IPI v5

On Tue, Jun 09, 2015 at 08:34:35AM -0700, Dave Hansen wrote:
> On 06/09/2015 05:43 AM, Ingo Molnar wrote:
> > +static char tlb_flush_target[PAGE_SIZE] __aligned(4096);
> > +static void fn_flush_tlb_one(void)
> > +{
> > +	unsigned long addr = (unsigned long)&tlb_flush_target;
> > +
> > +	tlb_flush_target[0]++;
> > +	__flush_tlb_one(addr);
> > +}
> 
> So we've got an increment of a variable in kernel memory (which is
> almost surely in the L1), then we flush that memory location, and repeat
> the increment.

BTW, Ingo, have you disabled direct mapping of kernel memory with 2M/1G
pages for the test? 

I'm just thinking if there is chance that the test shooting out 1G tlb
entry. In this case we're measure wrong thing.

-- 
 Kirill A. Shutemov
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