Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751884AbbEAQpg (ORCPT ); Fri, 1 May 2015 12:45:36 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:34912 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751263AbbEAQpd (ORCPT ); Fri, 1 May 2015 12:45:33 -0400 Date: Fri, 1 May 2015 18:45:26 +0200 From: Ingo Molnar To: Rik van Riel Cc: Andy Lutomirski , "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 Message-ID: <20150501164526.GB1548@gmail.com> 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> <20150501155912.GA451@gmail.com> <20150501162109.GA1091@gmail.com> <20150501163709.GC1327@gmail.com> <5543AC7E.5060602@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5543AC7E.5060602@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 Content-Length: 1396 Lines: 39 * Rik van Riel wrote: > On 05/01/2015 12:37 PM, Ingo Molnar wrote: > > > Also note that this bit in context_tracking_enter(): > > > > if (state == CONTEXT_USER) { > > trace_user_enter(0); > > vtime_user_enter(current); > > } > > > > > > is related to precise time measurement of user/kernel execution > > times, it's not needed by the scheduler at all, it's just exported > > to tooling. It's not fundamental to the scheduler. > > Any objections to the idea from the other thread to simply keep the > time accumulating in buffers in local_clock() units, and only update > the task vtime once a second or so? So I really think per syscall overhead is the wrong thing to do for anything that a common distro enables. I see very little use for such precise, high-freq measurements on normal systems - and abnormal systems could enable it dynamically just like they can enable syscall auditing. I.e. I don't mind the occasional crazy piece of code, as long as it does not hurt the innocent. Thanks, Ingo -- 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/