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[Xen-devel] Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT
From: Ingo Molnar <mingo@xxxxxxx>
Date: Tue, 27 Jan 2009 08:59:12 +0100
Cc: Zachary Amsden <zach@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "jeremy@xxxxxxxxxxxxx" <jeremy@xxxxxxxxxxxxx>, "rusty@xxxxxxxxxxxxxxx" <rusty@xxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, "chrisw@xxxxxxxxxxxx" <chrisw@xxxxxxxxxxxx>, "hpa@xxxxxxxxx" <hpa@xxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
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* Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

>>> Also, I just posted patches to get rid of all pvops calls when 
>>> fetching or setting flags in a pte, which I hope will help.
>> Sounds like it will help.
> ...but apparently not.


This is a very serious paravirt_ops slowdown affecting the native kernel's 
performance to the tune of 5-10% in certain workloads.

It's been about 2 years ago that paravirt_ops went upstream, when you told 
us that something like this would never happen, that paravirt_ops is 
designed so flexibly that it will never hinder the native kernel - and if 
it does it will be easy to fix it. Now is the time to fulfill that 


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