From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755036AbbINOK2 (ORCPT ); Mon, 14 Sep 2015 10:10:28 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:55548 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754048AbbINOK0 (ORCPT ); Mon, 14 Sep 2015 10:10:26 -0400 Date: Mon, 14 Sep 2015 16:10:12 +0200 From: Peter Zijlstra To: Waiman Long Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch , Davidlohr Bueso Subject: Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Message-ID: <20150914141012.GV18489@twins.programming.kicks-ass.net> References: <1441996658-62854-1-git-send-email-Waiman.Long@hpe.com> <1441996658-62854-7-git-send-email-Waiman.Long@hpe.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1441996658-62854-7-git-send-email-Waiman.Long@hpe.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 On Fri, Sep 11, 2015 at 02:37:38PM -0400, Waiman Long wrote: > In an overcommitted guest where some vCPUs have to be halted to make > forward progress in other areas, it is highly likely that a vCPU later > in the spinlock queue will be spinning while the ones earlier in the > queue would have been halted. The spinning in the later vCPUs is then > just a waste of precious CPU cycles because they are not going to > get the lock soon as the earlier ones have to be woken up and take > their turn to get the lock. > > This patch implements an adaptive spinning mechanism where the vCPU > will call pv_wait() if the following conditions are true: > > 1) the vCPU has not been halted before; > 2) the previous vCPU is not running. Why 1? For the mutex adaptive stuff we only care about the lock holder running, right?