From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction	abstraction
Date: Wed, 18 Jun 2008 22:03:43 -0700
Message-ID: <4859E8AF.30306@goop.org>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>, xen-devel <xen-devel@lists.xensource.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, kvm-devel <kvm-devel@lists.sourceforge.net>, x86@kernel.org, LKML <linux-kernel@vger.kernel.org>, Virtualization Mailing List <virtualization@lists.osdl.org>, Hugh Dickins <hugh@veritas.com>, Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
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Benjamin Herrenschmidt wrote:
> On Wed, 2008-06-18 at 17:24 -0700, Linus Torvalds wrote:
>   
>> On Wed, 18 Jun 2008, Jeremy Fitzhardinge wrote:
>>     
>>> Along the lines of:
>>>       
>> Hell no. There's a reason we have a special set_wrprotect() thing. We can 
>> do it more efficiently on native hardware by just clearing the bit 
>> atomically. No need to do the cmpxchg games.
>>     
>
> But we can't batch ... 
>   

Which architecture are you interested in?  If it isn't x86, you can 
probably get anything past Linus ;)

I'll do some measurements to see what effect the batchable 
ptep_set_wrprotect() has on native.  If it's significant, I'll propose 
making it conditional on CONFIG_PARAVIRT.

    J