From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932855AbWGARkZ (ORCPT ); Sat, 1 Jul 2006 13:40:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932943AbWGARkZ (ORCPT ); Sat, 1 Jul 2006 13:40:25 -0400 Received: from smtp107.mail.mud.yahoo.com ([209.191.85.217]:45473 "HELO smtp107.mail.mud.yahoo.com") by vger.kernel.org with SMTP id S932855AbWGARkZ (ORCPT ); Sat, 1 Jul 2006 13:40:25 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=bLNAofUm1X8oWYFmpkmgzyYyBRvGi66U7ClDfi4JYa2E0vkwbiA30OjyzG6djNhkJnAZN5Ql8BSGNaJnBtjcBmeXEw22KjpFEgnBtrBjiYBOKl50M+8h3EC8ckv6bWLfs1IURvMI0BjNeybRZBl3a+3qKMf9s5oj/6u06me7u5U= ; Message-ID: <44A6B387.80207@yahoo.com.au> Date: Sun, 02 Jul 2006 03:40:23 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Arjan van de Ven CC: linux-kernel@vger.kernel.org, akpm@osdl.org, ak@suse.de Subject: Re: [patch 0/2] sLeAZY FPU feature References: <1151773893.3195.45.camel@laptopd505.fenrus.org> In-Reply-To: <1151773893.3195.45.camel@laptopd505.fenrus.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven wrote: > Hi, > > the two patches in this series (the x86-64 on by me, the i386 one by > Chuck Ebbert) change how the lazy fpu feature works. In the current > situation, we are 100% lazy, meaning that after every context switch, > the application takes a trap on the first FPU use, which then restores > the FPU context. > > The sLeAZY FPU patch changes this behavior; if a process has used the > FPU for 5 stints at a row, the behavior becomes proactive and the FPU > context is restored during the regular context switch already. This > means we can avoid the trap. > > The underlying assumption is that if a process uses 5 times consecutive, > it's likely to do it the 6th and later times as well (eg it's not a > one-off behavior). > > There is a limit built in; this proactive behavior resets after 255 > times, so that when a process is long lived and chances behavior, it'll > still get the right behavior (for performance) after some time. > > Chuck measured a +/- 0.4% performance gain, and my experiments show a > similar improvement. What sort of test? Any idea of the results for a best case microbenchmark (something like two threads ping-pong a couple of futexes between them, in between doing a single FPU op) -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com