From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757582Ab1KQNsR (ORCPT ); Thu, 17 Nov 2011 08:48:17 -0500 Received: from casper.infradead.org ([85.118.1.10]:56258 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757428Ab1KQNsQ convert rfc822-to-8bit (ORCPT ); Thu, 17 Nov 2011 08:48:16 -0500 Subject: Re: [PATCH RFC] remove jump_label optimization for perf sched events From: Peter Zijlstra To: Avi Kivity Cc: Gleb Natapov , linux-kernel@vger.kernel.org, mingo@elte.hu, Jason Baron , rostedt , Thomas Gleixner Date: Thu, 17 Nov 2011 14:47:48 +0100 In-Reply-To: <4EC50B02.1060307@redhat.com> References: <20111117123029.GB16853@redhat.com> <1321534159.27735.33.camel@twins> <20111117130032.GC16853@redhat.com> <1321535413.27735.35.camel@twins> <4EC50B02.1060307@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1321537668.27735.38.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-11-17 at 15:24 +0200, Avi Kivity wrote: > On 11/17/2011 03:10 PM, Peter Zijlstra wrote: > > On Thu, 2011-11-17 at 15:00 +0200, Gleb Natapov wrote: > > > > > > That said, I'd much rather throttle this particular jump label than > > > > remove it altogether, some people really don't like all this scheduler > > > > hot path crap. > > > What about moving perf_event_task_sched() to sched_(in|out)_preempt_notifiers? > > > preempt notifiers checking is already on the scheduler hot path, so no > > > additional overhead for perf case. > > > > Same problem really, some people complain about the overhead of preempt > > notifiers, also not all kernels have those in. > > We could combine the two, sort-circuit preempt notifiers with jump > labels if empty && not much activity on them. Jump-labels are still more efficient, also I don't much like preempt notifiers. > > Futhermore I loathe notifier lists because they obscure wtf is done. > > That's life in a general purpose kernel, if everyone gets their hook in > to keep their code clean, the scheduler will bloat. Uhm, no. The bloat isn't different, the only difference is you can actually see it. So I very much prefer direct hooks. > An advantage of preempt notifiers is that you can make the perf code > modular. Yeah, and you know I loathe modules even more.