From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932978AbcETPFX (ORCPT ); Fri, 20 May 2016 11:05:23 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:41268 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750995AbcETPFV (ORCPT ); Fri, 20 May 2016 11:05:21 -0400 Date: Fri, 20 May 2016 17:05:05 +0200 From: Peter Zijlstra To: Davidlohr Bueso Cc: manfred@colorfullife.com, Waiman.Long@hpe.com, mingo@kernel.org, torvalds@linux-foundation.org, ggherdovich@suse.com, mgorman@techsingularity.net, linux-kernel@vger.kernel.org Subject: Re: sem_lock() vs qspinlocks Message-ID: <20160520150505.GG3193@twins.programming.kicks-ass.net> References: <20160520053926.GC31084@linux-uzut.site> <20160520074946.GA3193@twins.programming.kicks-ass.net> <20160520150049.GB7086@linux-uzut.site> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160520150049.GB7086@linux-uzut.site> 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 On Fri, May 20, 2016 at 08:00:49AM -0700, Davidlohr Bueso wrote: > On Fri, 20 May 2016, Peter Zijlstra wrote: > > >On Thu, May 19, 2016 at 10:39:26PM -0700, Davidlohr Bueso wrote: > >> In addition, this makes me wonder if queued_spin_is_locked() should then be: > >> > >>- return atomic_read(&lock->val); > >>+ return atomic_read(&lock->val) & _Q_LOCKED_MASK; > >> > >>And avoid considering pending waiters as locked. > > > >Probably > > Similarly, and I know you hate it, but afaict, then semantically > queued_spin_is_contended() ought to be: > > - return atomic_read(&lock->val) & ~_Q_LOCKED_MASK; > + return atomic_read(&lock->val); Nah, that would make it return true for (0,0,1), ie. uncontended locked.