From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH] x86 idle: repair large-server 50-watt idle-power regression Date: Thu, 19 Dec 2013 19:19:48 +0100 Message-ID: <20131219181948.GD32508@gmail.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=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <52B33640.3020204@zytor.com> Sender: stable-owner@vger.kernel.org To: "H. Peter Anvin" 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 * 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... For the minimal fix I don't think we should change it - but for v3.14 it looks like a speedup for the from-idle codepath, which is performance sensitive. ( It would also be nice to know whether MONITOR loads that cacheline into the CPUs cache, and in what state it loads it. ) Thanks, Ingo