From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757336AbbCMQV3 (ORCPT ); Fri, 13 Mar 2015 12:21:29 -0400 Received: from cantor2.suse.de ([195.135.220.15]:35058 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756764AbbCMQV2 (ORCPT ); Fri, 13 Mar 2015 12:21:28 -0400 Date: Fri, 13 Mar 2015 17:19:58 +0100 From: Borislav Petkov To: Oleg Nesterov Cc: Dave Hansen , Ingo Molnar , Andy Lutomirski , Linus Torvalds , Pekka Riikonen , Rik van Riel , Suresh Siddha , LKML , "Yu, Fenghua" , Quentin Casasnovas Subject: Re: [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in flush_thread() Message-ID: <20150313161958.GI31998@pd.tnic> References: <54F74F59.5070107@intel.com> <20150311173346.GB5032@redhat.com> <20150311173507.GF5032@redhat.com> <20150313105251.GD31998@pd.tnic> <20150313145542.GD21603@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150313145542.GD21603@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 13, 2015 at 03:55:42PM +0100, Oleg Nesterov wrote: > But please look at drop_init_fpu(). If eagerfpu == F it calls drop_fpu() and > this is what we need. flush_thread() already has the "if (!use_eager_fpu())", > we can shift drop_fpu() there. > > Otherwise, if eagerfpu == T, drop_init_fpu() does restore_init_xstate() and > this just burns CPU. Until flush_thread user_has_fpu/used_math this state > restore_init_xstate() is pointless, this state will be lost after preemption. Yeah, I was wondering why that's there. One example where drop_init_fpu() seems to make sense is __kernel_fpu_end(): kernel is done with FPU and current was using the FPU prior so let's restore it for the eagerfpu case. Thanks. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --