From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 35285ECAAD3 for ; Thu, 1 Sep 2022 18:28:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233374AbiIAS2N (ORCPT ); Thu, 1 Sep 2022 14:28:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58500 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231589AbiIAS2K (ORCPT ); Thu, 1 Sep 2022 14:28:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85A117CB55; Thu, 1 Sep 2022 11:28:08 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 228C860B9A; Thu, 1 Sep 2022 18:28:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B196C433C1; Thu, 1 Sep 2022 18:28:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1662056887; bh=YWgybhhjcjU5jUOQFDqICzPZy3pdwcYT9rfQcigKjhM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=T+LR2BL+97bJ7sMyH3KChJOTCU4OlNi+VkQ37FcDiIAB/QrMhPoRTUoF58W0czxyA bXiRHVhZna3yuZ9VL9khBxhItNHXqy7mRitSQ0quS9wRQ6G8Zao8aAz9JwCyPLy8ps f5owrifXe/RGWBAbwt9egDeSRmjeLGhXifeXoweJca0fxB8RIwr7Ilth6Nx0dyDxCR pEr4oYC6Ry4O8oyL3OeFS4GOPF0JgIaSGVaQ7ADN1RNPGIgnz6a4KvKgw2s9Dn1knV vcE0jZNrOQ++AjGF2+THrho+GJdbsweJhft3ikr9kGFe1kYyNDPC99lA7FTXYyuvCF B533uhhbUZkig== Date: Thu, 1 Sep 2022 20:28:04 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Joel Fernandes , Dietmar Eggemann , LKML , Rushikesh S Kadam , "Uladzislau Rezki (Sony)" , Neeraj upadhyay , Steven Rostedt , rcu , Vineeth Pillai Subject: Re: [PATCH v4 00/14] Implement call_rcu_lazy() and miscellaneous fixes Message-ID: <20220901182804.GA108007@lothringen> References: <20220830105324.GA71266@lothringen> <20220830114343.GS6159@paulmck-ThinkPad-P17-Gen-1> <20220830160316.GC71266@lothringen> <20220830162244.GA73392@lothringen> <20220830164634.GC6159@paulmck-ThinkPad-P17-Gen-1> <20220831152658.GA89704@lothringen> <20220901143907.GU6159@paulmck-ThinkPad-P17-Gen-1> <20220901145819.GB105556@lothringen> <0e8687de-bf45-5de6-c2f1-be6084991921@joelfernandes.org> <20220901164928.GZ6159@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220901164928.GZ6159@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 01, 2022 at 09:49:28AM -0700, Paul E. McKenney wrote: > > On 9/1/2022 10:58 AM, Frederic Weisbecker wrote: > > > On Thu, Sep 01, 2022 at 07:39:07AM -0700, Paul E. McKenney wrote: > > >> On Wed, Aug 31, 2022 at 05:26:58PM +0200, Frederic Weisbecker wrote: > > >>> On Tue, Aug 30, 2022 at 09:46:34AM -0700, Paul E. McKenney wrote: > > >>>>> Although who knows, may be some periodic file operation while idle are specific > > >>>>> to Android. I'll try to trace lazy callbacks while idle and the number of grace > > >>>>> periods associated. > > >>>> > > >>>> Sounds like a good start. > > >>>> > > >>>> And yes, we don't need to show that the whole !NOCB world needs this, > > >>>> just some significant portion of it. But we do need some decent evidence. > > >>>> After all, it is all too easy to do a whole lot of work and find that > > >>>> the expected benefits fail to materialize. > > >>> > > >>> So here is some quick test. I made a patch that replaces Joel's 1st patch > > >>> with an implementation of call_rcu_lazy() that queues lazy callbacks > > >>> through the regular call_rcu() way but it counts them in a lazy_count. > > >>> > > >>> Upon idle entry it reports whether the tick is retained solely by lazy > > >>> callbacks or not. > > >>> > > >>> I get periodic and frequent results on my idle test box, something must be > > >>> opening/closing some file periodically perhaps. > > >>> > > >>> Anyway the thing can be tested with this branch: > > >>> > > >>> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git > > >>> rcu/lazy-trace > > >>> > > >>> Excerpt: > > >>> > > >>> -0 [007] d..1. 414.226966: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle > > >>> -0 [007] d..1. 414.228271: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle > > >>> -0 [007] d..1. 414.232269: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle > > >>> -0 [007] d..1. 414.236269: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle > > >> > > >> Just to make sure that I understand, at this point, there is only the > > >> one lazy callback (and no non-lazy callbacks) on this CPU, and that > > >> CPU is therefore keeping the tick on only for the benefit of that one > > >> lazy callback. And for the above four traces, this is likely the same > > >> lazy callback. > > >> > > >> Did I get it right, or is there something else going on? > > > > > > Exactly that! > > Are these callbacks confined to the RCU_NEXT_READY_TAIL and RCU_NEXT_TAIL > segments, which are the ones that could (in theory) buffer callbacks > without having started a grace period? Or is it all the callbacks > regardless of segment? Ah good point! So I just excluded when those segments have callbacks and I now only get two tick retains every two seconds: -0 [007] d..1. 1111.893649: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1111.967575: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1113.895470: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1115.669446: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1115.898144: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1117.202833: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1117.900521: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1119.903327: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1120.766864: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1121.909182: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1122.441927: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1123.908911: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1125.868505: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1125.910898: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1127.682837: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1127.913719: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1129.916740: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1130.967052: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1131.919256: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1132.957163: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [000] d..1. 1133.630082: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1133.923053: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1135.927054: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1136.067679: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1137.652294: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1137.932546: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1138.200768: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1139.932573: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1141.167489: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1141.935232: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1143.440538: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle -0 [007] d..1. 1143.938560: rcu_needs_cpu: BAD: 1 lazy callbacks retaining dynticks-idle