From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753690Ab1LAUgh (ORCPT ); Thu, 1 Dec 2011 15:36:37 -0500 Received: from va3ehsobe006.messaging.microsoft.com ([216.32.180.16]:6816 "EHLO VA3EHSOBE007.bigfish.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751718Ab1LAUgg (ORCPT ); Thu, 1 Dec 2011 15:36:36 -0500 X-SpamScore: -12 X-BigFish: VPS-12(zz146fK1432N98dKzz1202hzz8275bhz2dh668h839h944h61h) X-Spam-TCS-SCL: 0:0 X-Forefront-Antispam-Report: CIP:163.181.249.108;KIP:(null);UIP:(null);IPV:NLI;H:ausb3twp01.amd.com;RD:none;EFVD:NLI X-WSS-ID: 0LVJL8U-01-IQX-02 X-M-MSG: Date: Thu, 1 Dec 2011 21:36:05 +0100 From: Hans Rosenfeld To: Andi Kleen CC: , , , , , , , , , Subject: Re: [PATCH 0/9] rework of extended state handling, LWP support Message-ID: <20111201203605.GB411@escobedo.osrc.amd.com> References: <1322570488-21798-1-git-send-email-hans.rosenfeld@amd.com> <20111130173745.GT878@escobedo.osrc.amd.com> <20111130215200.GS24062@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20111130215200.GS24062@one.firstfloor.org> Organization: Advanced Micro Devices GmbH, Einsteinring 24, 85609 Dornach b. Muenchen; Geschaeftsfuehrer: Andrew Bowd, Alberto Bozzo; Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen; Registergericht Muenchen, HRB Nr. 43632 User-Agent: Mutt/1.5.21 (2010-09-15) X-OriginatorOrg: amd.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 30, 2011 at 10:52:00PM +0100, Andi Kleen wrote: > On Wed, Nov 30, 2011 at 06:37:46PM +0100, Hans Rosenfeld wrote: > > On Tue, Nov 29, 2011 at 01:31:09PM -0800, Andi Kleen wrote: > > > Hans Rosenfeld writes: > > > > > > > > The lazy allocation of the xstate area has been removed. The support for > > > > extended states that cannot be saved/restored lazily, like AMD's LWP, > > > > need this. Since optimized library functions using SSE etc. are widely > > > > used today, most processes would have an xstate area anyway, making the > > > > memory overhead negligible. > > > > > > Do you have any data on that? It sounds dubious for specialized > > > workloads. > > > > What kind of specialized workload do you mean? > > Anything that doesn't do large memcpys/memsets: glibc only uses SSE > when you pass large buffers. And then doesn't use the FPU. And possibly > has lots of processes. > > Some older glibc did an unconditional FPU initialization at start, > but I believe that's long gone. Well, I can't comment on which glibc version does what exactly. But on the 64bit systems that I observed, _all_ processes had an xstate area allocated. That was not the case on 32bit, but I'd suspect that the 32bit distributions just aren't optimized for modern hardware. So I assume, if you have 10000s of processes on a legacy 32bit system that never do any FPU stuff or SSE optimizations, you might indeed waste a couple of megabytes. I don't think thats very realistic, but that's just my opinion. Hans -- %SYSTEM-F-ANARCHISM, The operating system has been overthrown