Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752676AbcDFSPe (ORCPT ); Wed, 6 Apr 2016 14:15:34 -0400 Received: from casper.infradead.org ([85.118.1.10]:42095 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752358AbcDFSPc (ORCPT ); Wed, 6 Apr 2016 14:15:32 -0400 Date: Wed, 6 Apr 2016 20:15:29 +0200 From: Peter Zijlstra To: Xunlei Pang Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Juri Lelli , Ingo Molnar , Steven Rostedt Subject: Re: [PATCH v2 2/2] rtmutex: Kill pi_waiters_leftmost from task_struct Message-ID: <20160406181529.GU3448@twins.programming.kicks-ass.net> References: <1459947556-12332-1-git-send-email-xlpang@redhat.com> <1459947556-12332-2-git-send-email-xlpang@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1459947556-12332-2-git-send-email-xlpang@redhat.com> 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: 678 Lines: 14 On Wed, Apr 06, 2016 at 08:59:16PM +0800, Xunlei Pang wrote: > Current code use pi_waiters_leftmost to record the leftmost waiter, > but actually it can be get directly from task_struct::pi_waiters > using rb_first(). The performance penalty introduced by rb_first() > should be fine, because normally there aren't that many rtmutexes > chained together for one task. > > We don't remove rt_mutex:pi_waiters_leftmost, as it is quite possible > for many tasks sharing one rtmutex. > > Thus, hereby remove pi_waiters_leftmost from task_struct. Again, I would like Thomas to chime in. This isn't about usual, but very much about worst case performance -- its RT code after all.