From owner-freebsd-current@FreeBSD.ORG Tue Jan 16 23:25:19 2007 Return-Path: X-Original-To: freebsd-current@freebsd.org Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 8835116A4B3 for ; Tue, 16 Jan 2007 23:25:19 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: from nf-out-0910.google.com (nf-out-0910.google.com [64.233.182.185]) by mx1.freebsd.org (Postfix) with ESMTP id 1A38213C459 for ; Tue, 16 Jan 2007 23:25:18 +0000 (UTC) (envelope-from asmrookie@gmail.com) Received: by nf-out-0910.google.com with SMTP id k27so25917nfc for ; Tue, 16 Jan 2007 15:25:18 -0800 (PST) DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:sender:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references:x-google-sender-auth; b=unHSmBAgHBl2oawC1ES6U9y1AHkT+ydZlxTw7hRj/fNl9TncmL0vLUd0KMpElLvdSzj4QkZaa6C1cv+HLfJBMIdYXsJmu23u1wwdyTH7P97Sxn/dOtLg80KoKHblMY77yuQlBhsceo/vvFtcJqdzrAd2jzyTKI6rq9aXY/418/4= Received: by 10.49.28.3 with SMTP id f3mr32690nfj.1168989914143; Tue, 16 Jan 2007 15:25:14 -0800 (PST) Received: by 10.48.238.9 with HTTP; Tue, 16 Jan 2007 15:25:14 -0800 (PST) Message-ID: <3bbf2fe10701161525j6ad9292y93502b8df0f67aa9@mail.gmail.com> Date: Wed, 17 Jan 2007 00:25:14 +0100 From: "Attilio Rao" Sender: asmrookie@gmail.com To: "Ivan Voras" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <3bbf2fe10607250813w8ff9e34pc505bf290e71758@mail.gmail.com> <3bbf2fe10607251004wf94e238xb5ea7a31c973817f@mail.gmail.com> <3bbf2fe10607261127p3f01a6c3w80027754f7d4e594@mail.gmail.com> <3bbf2fe10607281004o6727e976h19ee7e054876f914@mail.gmail.com> <3bbf2fe10701160851r79b04464m2cbdbb7f644b22b6@mail.gmail.com> <20070116154258.568e1aaf@pleiades.nextvenue.com> X-Google-Sender-Auth: 81be34d649c48d7f Cc: freebsd-current@freebsd.org, freebsd-arch@freebsd.org Subject: Re: [PATCH] Mantaining turnstile aligned to 128 bytes in i386 CPUs X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 16 Jan 2007 23:25:19 -0000 2007/1/17, Ivan Voras : > Kip Macy wrote: > > On 1/16/07, Ivan Voras wrote: > >> But it does seem to hurt the performance a bit - maybe it's time to add > >> another CPU option like I586_CPU and I686_CPU? > > > > Unless there is a compelling reason not to do so, I think that that > > would be a good idea. > > Maybe even someone finds a way to get optimized versions of memcpy in > the kernel :) > > I was thinking: AFAIK the only major stopper is context saving of the > various "auxiliary" registers - FPU, MMX, SSE, right? But is it an > all-or-nothing situation? I.e. does it make sense (can it be done?) to > just elect to save the MMX context? (AFAIK they are different registers > than SSE, but overlay FPU registers?) The idea is to save something > smaller than the full set. When I implemented fpu copy into the kernel I had a lot of thinking about this and I think it is possible at least with some restrictions. For example, for an xmm copy you would just save 8 registers content but you have to ensure no pending FPU exceptions will break your kernel and so you should preserve a clean copy of FPU state or, treact the corner cases you can get. For xmm, after some very productive discussions with bde@, we arrived at the conclusion that should be pretty safe to just have an 16 byte aligned buffer for registers saving (in this way you can use 8 movdqa for saving them) but I didn't end to play with it. (My implementation should deal with the problem of pinning the scheduler too, in order to avoid a wrong reading of per-cpu datas). Attilio -- Peace can only be achieved by understanding - A. Einstein