From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751705AbdKMDdu (ORCPT ); Sun, 12 Nov 2017 22:33:50 -0500 Received: from mx1.redhat.com ([209.132.183.28]:35310 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbdKMDds (ORCPT ); Sun, 12 Nov 2017 22:33:48 -0500 Date: Mon, 13 Nov 2017 11:33:43 +0800 From: Peter Xu To: Peter Zijlstra Cc: kvm@vger.kernel.org, Paolo Bonzini , Radim Kr??m???? , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] sched/swait: allow swake_up() to return Message-ID: <20171113033343.GA7603@xz-mi> References: <20171109091854.24367-1-peterx@redhat.com> <20171109091854.24367-2-peterx@redhat.com> <20171109102303.vsetymxc6rllomhh@hirez.programming.kicks-ass.net> <20171110071017.GH20627@xz-mi> <20171110080520.uslq75uucwlg5y7y@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20171110080520.uslq75uucwlg5y7y@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.1 (2017-09-22) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 13 Nov 2017 03:33:48 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 10, 2017 at 09:05:20AM +0100, Peter Zijlstra wrote: > On Fri, Nov 10, 2017 at 03:10:17PM +0800, Peter Xu wrote: > > I came to this when reading kvm_vcpu_wake_up(), so that only affects > > some statistic which may not be that critical. However I don't know > > whether there would be any other real use case that we would like to > > know exactly whether a call to [s]wake_up() has really done something > > or just returned with a NOP. > > > > Anyway, please let me know if you think the same change to wake_up() > > would be meaningful, otherwise I can drop this patch and post another > > KVM-only one to clean up the redundant callers of swait_active(), > > since even if we dropped that list check in 35a2897c2a30, we'll do > > that again in swake_up_locked(). > > See commits: > > 8cd641e3c7cb ("sched/wait: Add swq_has_sleeper()") > 5e0018b3e39e ("kvm: Serialize wq active checks in kvm_vcpu_wake_up()") > > > In any case, I don't think we want the change you propose. The numbers > don't mean much and there's no point in making all the callers in the > kernel slower for it. I see. And also we can introduce a new API for that if really needed. I'll repost with KVM only changes. Thanks for reviewing. -- Peter Xu