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 D8286C43217 for ; Thu, 1 Dec 2022 13:53:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231661AbiLANx4 (ORCPT ); Thu, 1 Dec 2022 08:53:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39102 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231604AbiLANxz (ORCPT ); Thu, 1 Dec 2022 08:53:55 -0500 Received: from mail-pl1-x630.google.com (mail-pl1-x630.google.com [IPv6:2607:f8b0:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5A14A1EAFC for ; Thu, 1 Dec 2022 05:53:54 -0800 (PST) Received: by mail-pl1-x630.google.com with SMTP id g10so1682452plo.11 for ; Thu, 01 Dec 2022 05:53:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=7fZGIGpys3hFomsbDWkYfnPyHGAIi2Fw65qRSE6pZbY=; b=bfJ2hC8WRKm2l9/l4BV7DkoGh2Km0kdbeXeRNCMZcnTerP5p2fKqdT2m/M6f6li1zO EkFsAaHx4KpROhRmnsFBxwR7xUxPEI0Wdof5cG9TKoAFAJOIbqj9pbQTa2B+6AJLZ9jP 8qs3Rwd5wJQm0bHfRXZ9fuqvObL7wx5mE+BjxkPE0Rt+OspqzguEZw/5Rjid/yHFdggX 6CybdIenz79ToNElLPg6X/tTbhUiAcxOP9zRRN3GKsqg9f46L63uLbnwyhF21NT35JFl zguarVGdiXEcla0XaHDonU6g/r9UCNRnFS7Vpko4trOrxRjVe6OBG7/n7iK39FqT1FbK IxNA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=7fZGIGpys3hFomsbDWkYfnPyHGAIi2Fw65qRSE6pZbY=; b=EsUlyd4eTgBYxyz0j/tmwRnizdRCB3llB9IZY1Yz5Sr0xjVFHWu/5wrd+QRF982+Kc XTx+SWvtI++h9XwjlvViwBZXGzoGAit1A0/lD8LlWk507xsiv52x2SENf4BeaKPFjZtd 7x/vFxdSTvI4fS/gAmRIBW6tVhxcXLSQwY+Xii6pF6RgqW7lXowJZF33w1JYKoQv6Srf rb/PmJ08wUvNLsD9siJS0VicmP3JD1wIlX/9T5MvPRM0TPa7Vyvu0LPPZQsN4DlV5DW1 FzzFX8eZwjTlePtBwLrH7ki6JsIQnxCt1fFTHuYDShhW/UsgLVlgySekZ8H8O3wGIrKt S+qA== X-Gm-Message-State: ANoB5pmRVaSXi3VrO4ZuJ9I6TwWons5bASTUYYNZ7+7ziF96ndYHFrny pGgLG63Z7sRJxs8AVAkObA== X-Google-Smtp-Source: AA0mqf6QFeSbonZEekIKE7vmqBaMFHf6xrK0NEB6IiZgfQdDAWPbQHtPwuSFjkPgeb1RbO4H4J6PYg== X-Received: by 2002:a17:902:7885:b0:189:1366:fba7 with SMTP id q5-20020a170902788500b001891366fba7mr48972001pll.45.1669902833861; Thu, 01 Dec 2022 05:53:53 -0800 (PST) Received: from piliu.users.ipa.redhat.com ([43.228.180.230]) by smtp.gmail.com with ESMTPSA id y5-20020a170902e18500b00174f7d10a03sm3620502pla.86.2022.12.01.05.53.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Dec 2022 05:53:53 -0800 (PST) Date: Thu, 1 Dec 2022 21:53:36 +0800 From: Pingfan Liu To: Boqun Feng Cc: rcu@vger.kernel.org, Lai Jiangshan , "Paul E. McKenney" , Frederic Weisbecker , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , "Zhang, Qiang1" Subject: Re: [PATCH] srcu: switch work func to allow concurrent gp Message-ID: References: <20221130083902.31577-1-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Wed, Nov 30, 2022 at 08:53:43AM -0800, Boqun Feng wrote: > On Wed, Nov 30, 2022 at 04:39:02PM +0800, Pingfan Liu wrote: > > ssp->srcu_cb_mutex is introduced to allow the other srcu state machine > > to advance as soon as possible. But according to the implement of > > workqueue, the same work_struct is serialized and can not run > > concurrently in fact. > > > > Quoting from Documentation/core-api/workqueue.rst > > " > > Non-reentrance Conditions > > ========================= > > > > Workqueue guarantees that a work item cannot be re-entrant if the following > > conditions hold after a work item gets queued: > > > > 1. The work function hasn't been changed. > > 2. No one queues the work item to another workqueue. > > 3. The work item hasn't been reinitiated. > > " > > > > To allow the concurrence to some extent, it can be achieved by changing > > the work function to break the conditions. As a result, when > > srcu_gp_end() releases srcu_gp_mutex, a new state machine can begin. > > > > Signed-off-by: Pingfan Liu > > Cc: Lai Jiangshan > > Cc: "Paul E. McKenney" > > Cc: Frederic Weisbecker > > Cc: Josh Triplett > > Cc: Steven Rostedt > > Cc: Mathieu Desnoyers > > Cc: "Zhang, Qiang1" > > To: rcu@vger.kernel.org > > --- > > kernel/rcu/srcutree.c | 19 +++++++++++++++++++ > > 1 file changed, 19 insertions(+) > > > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > > index 1c304fec89c0..56dd9bb2c8b8 100644 > > --- a/kernel/rcu/srcutree.c > > +++ b/kernel/rcu/srcutree.c > > @@ -75,6 +75,7 @@ static bool __read_mostly srcu_init_done; > > static void srcu_invoke_callbacks(struct work_struct *work); > > static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay); > > static void process_srcu(struct work_struct *work); > > +static void process_srcu_wrap(struct work_struct *work); > > static void srcu_delay_timer(struct timer_list *t); > > > > /* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */ > > @@ -763,6 +764,11 @@ static void srcu_gp_end(struct srcu_struct *ssp) > > cbdelay = 0; > > > > WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns()); > > + /* Change work func so work can be concurrent */ > > + if (ssp->work.work.func == process_srcu_wrap) > > + ssp->work.work.func = process_srcu; > > + else > > + ssp->work.work.func = process_srcu_wrap; > > This looks really hacky ;-) It would be good that workqueue has an API > to allow "resetting" a work. > Indeed, it is hacky and it can be done by using alternative work_struct so that from the workqueue API, it is intact. > Do you have any number of the potential performance improvement? > I will try to bring out one. But the result may heavily depend on the test case. Thanks, Pingfan > Regards, > Boqun > > > rcu_seq_end(&ssp->srcu_gp_seq); > > gpseq = rcu_seq_current(&ssp->srcu_gp_seq); > > if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq)) > > @@ -1637,6 +1643,19 @@ static void process_srcu(struct work_struct *work) > > srcu_reschedule(ssp, curdelay); > > } > > > > +/* > > + * The ssp->work is expected to be concurrent to some extent, but the current > > + * workqueue does not support the concurrence on the same work. (Refer to the > > + * section "Non-reentrance Conditions" in the file workqueue.rst) > > + * Resolving it by changing the work func. > > + * > > + * Prevent compilering from optimizing out it. > > + */ > > +static __used void process_srcu_wrap(struct work_struct *work) > > +{ > > + process_srcu(work); > > +} > > + > > void srcutorture_get_gp_data(enum rcutorture_type test_type, > > struct srcu_struct *ssp, int *flags, > > unsigned long *gp_seq) > > -- > > 2.31.1 > >