linux-kernel - Re: [patch 1/2] x86,pat Update the page flags for memtype atomically instead of using memtype

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Date:	Wed, 17 Mar 2010 08:21:16 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"holt@....com" <holt@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [patch 1/2] x86,pat Update the page flags for memtype
 atomically instead of using memtype_lock. -V3

On Mon, 2010-03-15 at 06:21 -0700, holt@....com wrote:
> While testing an application using the xpmem (out of kernel) driver, we
> noticed a significant page fault rate reduction of x86_64 with respect
> to ia64.  For one test running with 32 cpus, one thread per cpu, it
> took 01:08 for each of the threads to vm_insert_pfn 2GB worth of pages.
> For the same test running on 256 cpus, one thread per cpu, it took 14:48
> to vm_insert_pfn 2 GB worth of pages.
> 
> The slowdown was tracked to lookup_memtype which acquires the
> spinlock memtype_lock.  This heavily contended lock was slowing down
> vm_insert_pfn().
> 
> With the cmpxchg on page->flags method, both the 32 cpu and 256 cpu
> cases take approx 00:01.3 seconds to complete.

Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>

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