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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4315C46499 for ; Fri, 5 Jul 2019 20:00:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 737C52133F for ; Fri, 5 Jul 2019 20:00:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="aL5g/htZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725894AbfGEUAH (ORCPT ); Fri, 5 Jul 2019 16:00:07 -0400 Received: from mail-pl1-f193.google.com ([209.85.214.193]:46218 "EHLO mail-pl1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbfGEUAH (ORCPT ); Fri, 5 Jul 2019 16:00:07 -0400 Received: by mail-pl1-f193.google.com with SMTP id c2so3470357plz.13 for ; Fri, 05 Jul 2019 13:00:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=OPAXAnhkT4uZSctQZWV1C46mb9I9NT/kztcwNDiggR4=; b=aL5g/htZRlrExROSvMSyc7IoQawmcZBzqQ1QXr+jI6w+an8O5JeLOtzhgx0liosdmZ ZqMaJgfyMR7GUq+OQwh9jmlw5EBkSG3WmUMVQ8vXqg9U/CleOoQk/r0/qXq+tXDQx1zJ c40N8zuZhbkyznqguXC2dtjemBs0gvTgNR60M= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=OPAXAnhkT4uZSctQZWV1C46mb9I9NT/kztcwNDiggR4=; b=MlDMySHOn0hzg5KyEAoIC7ckU1MZC7p49YZ7XMaUCt3AXlCfjluJw3e2h+vI4ac8RA 5BWbBA8efmoJKSP/LWdM+WOGe/eyjpx/gvn1p7zRUPOAJ8dx/avR8T2EG4uSQWe5AcxW VlDq0aPG+Cs+9XLqE043qNB26Uj1UO8U6XgiqXcNR7JXczULhY2R1QGA+M93XnME0qcv m07+JhbApZKofRviZbDNGM/09Ayu80AMMBMfTe5mIrocXldlpBDIAxhBaULqXzCVSxry zc3FBmfI1CZ70Y3c0CjDk5OrmcPXRf3xlB70JptXimPg0LKgyA/aL4/Gtwyr9XvFY+Yv GkTQ== X-Gm-Message-State: APjAAAWU6ckTTGmmSc+T4W/ZrCp8DFm+vrY6TI45icpvbgTu+wLPoO1D iHYHw4XOtmlVlKRQ5wLr1SOGMQ== X-Google-Smtp-Source: APXvYqxW6nCn29Nvym1Fo35HLgteQzwq1tpxscj8RCQfX4kSwdj2jd1uyXxG1H60u35FxFcc89ZY+w== X-Received: by 2002:a17:902:724a:: with SMTP id c10mr7127331pll.298.1562356806046; Fri, 05 Jul 2019 13:00:06 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id d16sm3195281pgb.4.2019.07.05.13.00.04 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Fri, 05 Jul 2019 13:00:05 -0700 (PDT) Date: Fri, 5 Jul 2019 16:00:03 -0400 From: Joel Fernandes To: "Paul E. McKenney" Cc: Byungchul Park , linux-kernel@vger.kernel.org, Davidlohr Bueso , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt , kernel-team@android.com Subject: Re: [PATCH] rcuperf: Make rcuperf kernel test more robust for !expedited mode Message-ID: <20190705200003.GB134527@google.com> References: <20190704043431.208689-1-joel@joelfernandes.org> <20190704174044.GK26519@linux.ibm.com> <20190705035231.GA31088@X58A-UD3R> <20190705122450.GA82532@google.com> <20190705150932.GO26519@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190705150932.GO26519@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Jul 05, 2019 at 08:09:32AM -0700, Paul E. McKenney wrote: > On Fri, Jul 05, 2019 at 08:24:50AM -0400, Joel Fernandes wrote: > > On Fri, Jul 05, 2019 at 12:52:31PM +0900, Byungchul Park wrote: > > > On Thu, Jul 04, 2019 at 10:40:44AM -0700, Paul E. McKenney wrote: > > > > On Thu, Jul 04, 2019 at 12:34:30AM -0400, Joel Fernandes (Google) wrote: > > > > > It is possible that the rcuperf kernel test runs concurrently with init > > > > > starting up. During this time, the system is running all grace periods > > > > > as expedited. However, rcuperf can also be run for normal GP tests. > > > > > Right now, it depends on a holdoff time before starting the test to > > > > > ensure grace periods start later. This works fine with the default > > > > > holdoff time however it is not robust in situations where init takes > > > > > greater than the holdoff time to finish running. Or, as in my case: > > > > > > > > > > I modified the rcuperf test locally to also run a thread that did > > > > > preempt disable/enable in a loop. This had the effect of slowing down > > > > > init. The end result was that the "batches:" counter in rcuperf was 0 > > > > > causing a division by 0 error in the results. This counter was 0 because > > > > > only expedited GPs seem to happen, not normal ones which led to the > > > > > rcu_state.gp_seq counter remaining constant across grace periods which > > > > > unexpectedly happen to be expedited. The system was running expedited > > > > > RCU all the time because rcu_unexpedited_gp() would not have run yet > > > > > from init. In other words, the test would concurrently with init > > > > > booting in expedited GP mode. > > > > > > > > > > To fix this properly, let us check if system_state if SYSTEM_RUNNING > > > > > is set before starting the test. The system_state approximately aligns > > > > > > Just minor typo.. > > > > > > To fix this properly, let us check if system_state if SYSTEM_RUNNING > > > is set before starting the test. ... > > > > > > Should be > > > > > > To fix this properly, let us check if system_state is set to > > > SYSTEM_RUNNING before starting the test. ... > > > > That's a fair point. I wonder if Paul already fixed it up in his tree, > > however I am happy to resend if he hasn't. Paul, how would you like to handle > > this commit log nit? > > > > it is just 'if ..' to 'is SYSTEM_RUNNING' > > It now reads as follows: > > To fix this properly, this commit waits until system_state is > set to SYSTEM_RUNNING before starting the test. This change is > made just before kernel_init() invokes rcu_end_inkernel_boot(), > and this latter is what turns off boot-time expediting of RCU > grace periods. Ok, looks good to me, thanks. And for below patch, Reviewed-by: Joel Fernandes (Google) > I dropped the last paragraph about late_initcall(). And I suspect that > the last clause from rcu_gp_is_expedited() can be dropped: > > bool rcu_gp_is_expedited(void) > { > return rcu_expedited || atomic_read(&rcu_expedited_nesting) || > rcu_scheduler_active == RCU_SCHEDULER_INIT; > } > > This is because rcu_expedited_nesting is initialized to 1, and is > decremented in rcu_end_inkernel_boot(), which is called long after > rcu_scheduler_active has been set to RCU_SCHEDULER_RUNNING, which > happens at core_initcall() time. So if the last clause says "true", > so does the second-to-last clause. > > The similar check in rcu_gp_is_normal() is still need, however, to allow > the power-management subsystem to invoke synchronize_rcu() just after > the scheduler has been initialized, but before RCU is aware of this. > > So, how about the commit shown below? > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 1f7e72efe3c761c2b34da7b59e01ad69c657db10 > Author: Paul E. McKenney > Date: Fri Jul 5 08:05:10 2019 -0700 > > rcu: Remove redundant "if" condition from rcu_gp_is_expedited() > > Because rcu_expedited_nesting is initialized to 1 and not decremented > until just before init is spawned, rcu_expedited_nesting is guaranteed > to be non-zero whenever rcu_scheduler_active == RCU_SCHEDULER_INIT. > This commit therefore removes this redundant "if" equality test. > > Signed-off-by: Paul E. McKenney > > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > index 249517058b13..64e9cc8609e7 100644 > --- a/kernel/rcu/update.c > +++ b/kernel/rcu/update.c > @@ -136,8 +136,7 @@ static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1); > */ > bool rcu_gp_is_expedited(void) > { > - return rcu_expedited || atomic_read(&rcu_expedited_nesting) || > - rcu_scheduler_active == RCU_SCHEDULER_INIT; > + return rcu_expedited || atomic_read(&rcu_expedited_nesting); > } > EXPORT_SYMBOL_GPL(rcu_gp_is_expedited); > >