linux-kernel - Re: [patch 0/2] x86,pat: Reduce contention on the memtype

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Message-ID: <alpine.LFD.2.00.1003241214370.3147@localhost.localdomain>
Date:	Wed, 24 Mar 2010 12:15:19 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Robin Holt <holt@....com>
cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...il.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	x86@...nel.org, Rafael Wysocki <rjw@...ell.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [patch 0/2] x86,pat: Reduce contention on the memtype_lock -V4

On Wed, 24 Mar 2010, Robin Holt wrote:
> On Wed, Mar 24, 2010 at 03:16:14AM +0100, Andi Kleen wrote:
> > holt@....com writes:
> > 
> > > Tracking memtype on x86 uses a single global spin_lock for either reading
> > > or changing the memory type.  This includes changes made to page flags
> > > which is perfectly parallel.
> > >
> > > Part one of the patchset makes the page-based tracking use cmpxchg
> > > without a need for a lock.
> > >
> > > Part two of the patchset converts the spin_lock into a read/write lock.
> > 
> > I'm curious: in what workloads did you see contention?
> > 
> > For any scalability patches it would be always good to have a description
> > of the workload.
> 
> It was a job using xpmem (an out of tree kernel module) which uses
> vm_insert_pfn to establish ptes.  The scalability issues were shown
> in the first patch.  I do not have any test which shows a performance
> difference  with the spin_lock to rw_lock conversion.

And what's exactly the point of converting it to a rw_lock then ?

Thanks,

	tglx
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