Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1945901AbbEVNsR (ORCPT ); Fri, 22 May 2015 09:48:17 -0400 Received: from casper.infradead.org ([85.118.1.10]:49478 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756927AbbEVNsP (ORCPT ); Fri, 22 May 2015 09:48:15 -0400 Date: Fri, 22 May 2015 15:48:11 +0200 From: Peter Zijlstra To: Stephane Eranian Cc: Ingo Molnar , Vince Weaver , Jiri Olsa , LKML Subject: Re: [PATCH 02/10] perf/x86: Improve HT workaround GP counter constraint Message-ID: <20150522134811.GI3644@twins.programming.kicks-ass.net> References: <20150522125344.GA3644@twins.programming.kicks-ass.net> <20150522125908.GB3644@twins.programming.kicks-ass.net> <20150522132534.GD3644@twins.programming.kicks-ass.net> <20150522133636.GE3644@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 1339 Lines: 29 On Fri, May 22, 2015 at 06:40:49AM -0700, Stephane Eranian wrote: > On Fri, May 22, 2015 at 6:36 AM, Peter Zijlstra wrote: > > On Fri, May 22, 2015 at 06:29:47AM -0700, Stephane Eranian wrote: > >> On Fri, May 22, 2015 at 6:25 AM, Peter Zijlstra wrote: > >> > On Fri, May 22, 2015 at 06:07:00AM -0700, Stephane Eranian wrote: > >> >> > >> >> One other thing I noticed is that the --n_excl needs to be protected by the > >> >> excl_cntrs->lock in put_excl_constraints(). > >> > > >> > Nah, its strictly per cpu. > >> > >> No. the excl_cntrs struct is pointed to by cpuc but it is shared between the > >> sibling HT. Otherwise this would not work! > > > > n_excl is per cpuc, see the trickery with has_exclusive vs > > exclusive_present on how I avoid the lock. > > Yes, but I believe you create a store forward penalty with this. > You store 16bits and you load 32 bits on the same cache line. The store and load are fairly well spaced -- the entire scheduling fast path is in between. And such a penalty is still cheap compared to locking, no? -- 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/