From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755149AbaEVNJj (ORCPT ); Thu, 22 May 2014 09:09:39 -0400 Received: from casper.infradead.org ([85.118.1.10]:45357 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755115AbaEVNJh (ORCPT ); Thu, 22 May 2014 09:09:37 -0400 Date: Thu, 22 May 2014 15:09:31 +0200 From: Peter Zijlstra To: Andy Lutomirski Cc: Ingo Molnar , Thomas Gleixner , nicolas.pitre@linaro.org, daniel.lezcano@linaro.org, Mike Galbraith , "linux-kernel@vger.kernel.org" Subject: Re: [RFC][PATCH 0/8] sched,idle: need resched polling rework Message-ID: <20140522130931.GV13658@twins.programming.kicks-ass.net> References: <20140411134243.160989490@infradead.org> <20140522125818.GV30445@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="wnBGVoaGQwxWUIo6" Content-Disposition: inline In-Reply-To: <20140522125818.GV30445@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --wnBGVoaGQwxWUIo6 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Thu, May 22, 2014 at 02:58:18PM +0200, Peter Zijlstra wrote: > --- > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 4ea7b3f1a087..a5da85fb3570 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -546,12 +546,38 @@ static bool set_nr_and_not_polling(struct task_struct *p) > struct thread_info *ti = task_thread_info(p); > return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG); > } > + > +/* > + * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set. > + */ > +static bool set_nr_if_polling(struct task_struct *p) > +{ > + struct thread_info *ti = task_thread_info(p); > + typeof(ti->flags) old, val = ti->flags; > + > + for (;;) { > + if (!(val & _TIF_POLLING_NRFLAG)) > + return false; > + if (val & _TIF_NEED_RESCHED) > + return true; Hmm, I think this is racy, false would be safer. If its already set we might already be past the sched_ttwu_pending() invocation, while if its clear and we're the one to set it, we're guaranteed not. > + old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED); > + if (old == val) > + return true; > + val = old; > + } > +} --wnBGVoaGQwxWUIo6 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJTffcLAAoJEHZH4aRLwOS6B6UP/jA0mCwUbk0wGw4LP+d7DT1z szsmQwWRa/4U01WhCzeerQa8/8nONevHdkhgaIQeCfncI/a46hLgSZtKj9Y71jON IGEbOYviKDDPzC5YsBI55nDLf3QTiyYMQAVh+hsiqLptfwkhm89w0UU8I6UR7zmh 4w6CVN4/ytuXOT+rcaZhKnU+5f+aT2avJLH+GLBJt0IW2hYZ7OUihZzVW3M5bMPh GnAN3XtfgYHKOrj/d1quCymSNAXp34JDxbz/UY0PSin9wDiRS5JvKz6boLUsRnqp 7y/w6ZiL/Sg5jBH4vZGlUsU5Hkz9IMe2MGjgj6R+JDdUFiih+CK9N+JVpEHSKN4k d39DmSHeStegdDYQK+0VNzFV6FhoL9P3KpbDy0cPH2OgFABeAGC5HDuPVKy3oT2O GmANJiyrInomFG1JLi0wSkdW4o8ELWf0XN6xCbZhqE1l1DzdvDabb+hj/7U5cQnc XBznDNxQJV9K3XRzkQmzWpaPFewyVjQhVwuikrxnRJoK0FQW5k108BYBdeCjcf6i 1qwO91PJpkju1fn5t6WlK06cOZONWIDCOupYt4hF2VqcEPi7tbsz3dUDGvcC+tf8 LdklZIyJmLXNItlFZrickZ7gv52ew7s/9YLLxD1NLlqTcPELtt4aeAaWpByVzwjp 37kHxy0LCHXpYA8rysb6 =TkRa -----END PGP SIGNATURE----- --wnBGVoaGQwxWUIo6--