linux-kernel - Re: lmbench lat_mmap slowdown with CONFIG

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Message-ID: <20090127075912.GA6551@elte.hu>
Date:	Tue, 27 Jan 2009 08:59:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Zachary Amsden <zach@...are.com>, Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"jeremy@...source.com" <jeremy@...source.com>,
	"chrisw@...s-sol.org" <chrisw@...s-sol.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT


* Jeremy Fitzhardinge <jeremy@...p.org> 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.

ping?

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 
promise.

	Ingo
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