From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751376AbcETUrz (ORCPT ); Fri, 20 May 2016 16:47:55 -0400 Received: from mail-bl2on0103.outbound.protection.outlook.com ([65.55.169.103]:56136 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750869AbcETUrx (ORCPT ); Fri, 20 May 2016 16:47:53 -0400 Authentication-Results: stgolabs.net; dkim=none (message not signed) header.d=none;stgolabs.net; dmarc=none action=none header.from=hpe.com; Message-ID: <573F77EF.3020409@hpe.com> Date: Fri, 20 May 2016 16:47:43 -0400 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Davidlohr Bueso CC: Peter Zijlstra , , , , , , Subject: Re: sem_lock() vs qspinlocks References: <20160520053926.GC31084@linux-uzut.site> <20160520074946.GA3193@twins.programming.kicks-ass.net> <20160520150049.GB7086@linux-uzut.site> In-Reply-To: <20160520150049.GB7086@linux-uzut.site> Content-Type: text/plain; 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>>> + 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); > > Thanks, > Davidlohr Looking for contended lock, you need to consider the lock waiters also. So looking at the whole word is right. Cheers, Longman