From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754285AbcA0LQx (ORCPT ); Wed, 27 Jan 2016 06:16:53 -0500 Received: from www.linutronix.de ([62.245.132.108]:42581 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753982AbcA0LQv (ORCPT ); Wed, 27 Jan 2016 06:16:51 -0500 Date: Wed, 27 Jan 2016 12:15:47 +0100 (CET) From: Thomas Gleixner To: Arjan van de Ven cc: John Stultz , lkml , Ruchi Kandoi , Oren Laadan , Micha Kalfon , Rom Lemarchand , Android Kernel Team Subject: Re: [RFC][PATCH v2] prctl: Add PR_SET_TIMERSLACK_PID for setting timer slack of an arbitrary thread. In-Reply-To: <56A774D8.5020401@linux.intel.com> Message-ID: References: <1453782484-3887-1-git-send-email-john.stultz@linaro.org> <56A774D8.5020401@linux.intel.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 26 Jan 2016, Arjan van de Ven wrote: > On 1/25/2016 8:28 PM, John Stultz wrote: > > From: Ruchi Kandoi > > > > This allows power/performance management software to set timer > > slack for other threads according to its policy for the thread > > (such as when the thread is designated foreground vs. background > > activity) > > > > Second argument is similar to PR_SET_TIMERSLACK, if non-zero > > then the slack is set to that value otherwise sets it to the > > default for the thread. > > > > Takes PID of the thread as the third argument. > > > > This interface checks that the calling task has permissions to > > to use PTRACE_MODE_ATTACH on the target task, so that we can > > ensure arbitrary apps do not change the timer slack for other > > apps. > > Acked-by: Arjan van de Ven > > only slight concern is the locking around the value of the field in the task > struct, > but nobody does read-modify-write on it, so they'll get either the new or the > old version, > which should be ok. > > (until now only the local thread would touch the field, and if you're setting > it, by definition > you're not going to sleep yet, so you're not using the field) Even if you access it remote, it's a non issue. The task will see either the old or the new value. Which is equally true when you add locking around the write. Thanks, tglx