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 84A8FECAAD1 for ; Thu, 1 Sep 2022 14:58:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233846AbiIAO63 (ORCPT ); Thu, 1 Sep 2022 10:58:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232713AbiIAO6Z (ORCPT ); Thu, 1 Sep 2022 10:58:25 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D468C75CE3; Thu, 1 Sep 2022 07:58:23 -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 6FAEA61DF3; Thu, 1 Sep 2022 14:58:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 50988C433C1; Thu, 1 Sep 2022 14:58:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1662044302; bh=En7apUiUy36ywZsUgJ3gviiKGdFpGXtXpQxMMA0VXF0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jX9tR1swI2COSnSV5z/gdyF496mf2T4tk9tBw3Lc9WjSgDeNA1THG+NthmE8IDNmq SCMiJOEYCvpfZG/F2XiLNgDIJyNBfKMj0f1KXV+ohkMdYaNatuUdw/9pHSEXtl+9X6 +8AnmTmJEd+gN4s0KGHGN/4J2nnrIEL9s5kYC18ZMEblyT87ohSnEutsxQ+43lHzSZ HbVdwRokcsNDUq39MKTyu52ibu0O9ezEFOw+acdTwpLUE1O9JsJhwe2RKnAFYLEypz bdKhhYftgTH7Nw6QiJWc1rG5O8Utz4uSCIZ2tCee3o5rdH7I+LRYf6ihWa1G9MQU+1 UnsikXDEyMD/g== Date: Thu, 1 Sep 2022 16:58:19 +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: <20220901145819.GB105556@lothringen> References: <20220829194622.GA58291@lothringen> <20220829204202.GQ6159@paulmck-ThinkPad-P17-Gen-1> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220901143907.GU6159@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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! Thanks.