From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zachary Amsden <zach@vmware.com>
Subject: Re: [patch 28/34] Xen-pv_ops: Xen SMP guest support
Date: Wed, 14 Mar 2007 12:23:43 -0800
Message-ID: <45F859CF.8040100@vmware.com>
References: <20070313233017.933601256@goop.org> <20070313233034.586018620@goop.org> <20070314132820.GL6209@kvack.org>
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To: Benjamin LaHaise <bcrl@kvack.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, Andi Kleen <ak@muc.de>, Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, xen-devel@lists.xensource.com, Chris Wright <chrisw@sous-sol.org>, Rusty Russell <rusty@rustcorp.com.au>, Ingo Molnar <mingo@redhat.com>, Andi Kleen <ak@suse.de>
List-Id: virtualization@lists.linuxfoundation.org

Benjamin LaHaise wrote:
>   
>> +/*
>> + * We aggressively remove defunct pgd from cr3. We execute unmap_vmas()
>> + * *much* faster this way.
>> + */
>>     
>
> Are you switching mms in order to avoid all of the overhead associated with 
> flushing an active mm during task exit?  If so, it makes much more sense to 
> do this in the generic helper, as it should be a win on x86 and x86-64 
> where switching to init_mm is relatively low cost given the support for 
> global pages.  I'll run some tests on a couple of systems this evening and 
> post the results.
>   

I tried this experiment on both x86 and x86-64 and I recall not seeing 
any effect.  The mmu_gather optimization does most of this already.

Zach