From mboxrd@z Thu Jan 1 00:00:00 1970 From: "H. Peter Anvin" Subject: Re: [PATCH] x86 idle: repair large-server 50-watt idle-power regression Date: Thu, 19 Dec 2013 10:19:22 -0800 Message-ID: <52B338AA.1020307@zytor.com> References: <20131219122257.GC11279@gmail.com> <52B316FF.50906@zytor.com> <20131219160210.GA28426@gmail.com> <52B31B21.6010901@zytor.com> <20131219162136.GM16438@laptop.programming.kicks-ass.net> <52B323BE.7090108@zytor.com> <20131219170741.GB30382@gmail.com> <52B33640.3020204@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <52B33640.3020204@zytor.com> Sender: stable-owner@vger.kernel.org To: Ingo Molnar Cc: Peter Zijlstra , Len Brown , x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Len Brown , stable@vger.kernel.org, Linus Torvalds , Thomas Gleixner , Mike Galbraith , Borislav Petkov List-Id: linux-pm@vger.kernel.org On 12/19/2013 10:09 AM, H. Peter Anvin wrote: > On 12/19/2013 09:07 AM, Ingo Molnar wrote: >> >> Likewise, having a barrier before the MONITOR looks sensible as well. >> Having it _after_ monitor looks weird and is probably wrong. [It might >> have been the effects of someone seeing the spurious wakeup problems >> with realizing the true source, or so.] >> > > Does anyone know the history of this barrier after the monitor? I know > Len is looking for a minimal patchset that can go into -stable, and it > seems prudent to not preturb the code more than necessary, but going > forward it would be nice to know... > Hmm... it *looks* like it is intended to be part of the construct: smp_mb(); if (!need_resched()) ... I found a note in the HLT variant of the function saying: /* * TS_POLLING-cleared state must be visible before we * test NEED_RESCHED: */ ... which presumably has been copied elsewhere. -hpa