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Date: Sun, 21 Jun 2015 23:22:31 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH 0/3] TLB flush multiple pages per IPI v5
Message-ID: <20150621202231.GB6766@node.dhcp.inet.fi>
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To: Dave Hansen <dave.hansen@intel.com>, Ingo Molnar <mingo@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>, Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>, Minchan Kim <minchan@kernel.org>, Andi Kleen <andi@firstfloor.org>, H Peter Anvin <hpa@zytor.com>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Thomas Gleixner <tglx@linutronix.de>

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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