Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751363AbbEGPsU (ORCPT ); Thu, 7 May 2015 11:48:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32782 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751121AbbEGPsT (ORCPT ); Thu, 7 May 2015 11:48:19 -0400 Message-ID: <554B891A.9040109@redhat.com> Date: Thu, 07 May 2015 11:47:38 -0400 From: Rik van Riel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Ingo Molnar , Frederic Weisbecker CC: Andy Lutomirski , Mike Galbraith , "linux-kernel@vger.kernel.org" , X86 ML , williams@redhat.com, Andrew Lutomirski , fweisbec@redhat.com, Peter Zijlstra , Heiko Carstens , Thomas Gleixner , Ingo Molnar , Paolo Bonzini Subject: Re: [PATCH 3/3] context_tracking,x86: remove extraneous irq disable & enable from context tracking on syscall entry References: <1430429035-25563-1-git-send-email-riel@redhat.com> <1430429035-25563-4-git-send-email-riel@redhat.com> <20150501064044.GA18957@gmail.com> <554399D1.6010405@redhat.com> <1430659432.4233.3.camel@gmail.com> <55465B2D.6010300@redhat.com> <55466E72.8060602@redhat.com> <20150507104845.GB14924@gmail.com> <20150507121848.GB32271@lerouge> <20150507122913.GA17443@gmail.com> In-Reply-To: <20150507122913.GA17443@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1361 Lines: 36 On 05/07/2015 08:29 AM, Ingo Molnar wrote: > > * Frederic Weisbecker wrote: > >>>> We cannot take the lock_trace(task) from irq context, and we >>>> probably do not need to anyway, since we do not care about a >>>> precise stack trace for the task. >>> >>> So one worry with this and similar approaches of statistically >>> detecting user mode would be the fact that on the way out to >>> user-space we don't really destroy the previous call trace - we >>> just pop off the stack (non-destructively), restore RIPs and are >>> gone. >>> >>> We'll need that percpu flag I suspect. >> >> Note we have the context tracking state which tells where the >> current task is: user/system/guest. > > Yes, but that overhead is what I'm suggesting we get rid of, I thought > Rik was trying to find a mechanism that would be independent of that? One thing at a time :) I am working on the timer sampling stuff, which should be easy to adapt to a different user/system/guest/irq/softirq/... tracking thing, if somebody else comes up with a more efficient way to do that. -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/