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=-6.8 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,URIBL_BLOCKED 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 01FB8C433DF for ; Thu, 28 May 2020 01:35:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D071D207BC for ; Thu, 28 May 2020 01:35:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="lVcCoEvH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726761AbgE1Bfn (ORCPT ); Wed, 27 May 2020 21:35:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35140 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726701AbgE1Bfm (ORCPT ); Wed, 27 May 2020 21:35:42 -0400 Received: from mail-qt1-x841.google.com (mail-qt1-x841.google.com [IPv6:2607:f8b0:4864:20::841]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 53FBCC05BD1E for ; Wed, 27 May 2020 18:35:41 -0700 (PDT) Received: by mail-qt1-x841.google.com with SMTP id y1so10333195qtv.12 for ; Wed, 27 May 2020 18:35:41 -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; bh=kdRDIUud9vdh99K7Eu/EqGMgSstVkExNLQUlmKuT+XE=; b=lVcCoEvHHzK6BC2/IL8DEorOj1zfU8FM/FFH0JZW5EPmI5W9+BCLzWrHQ0cR0aRcLv hy30GVtibgm9CCMA/xMhNu/gqV+CjItzrLcj3hDMxj6Gab9PbBrmLUFmh4BICFw13YNS 3skYqmhMj+bOTA4rswSY0pUwACTGEtFqMfIXA= 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; bh=kdRDIUud9vdh99K7Eu/EqGMgSstVkExNLQUlmKuT+XE=; b=btcY1R51M7UqWmL7nKQs9BrUexgpATX8tSyhybLxEuIFpYddh/bEkYRlfert+sqiiO kU8QN7pYb4Y6M1ip18oj9xIkBU+wGXVd4xBJm4BJuVD6CXt60Tyez2QXQM3Qc2lZ8dg4 57vME9PEFQjxDTM/qykBoAloFxkVzoUC4oNUEJrxY/mPiBRBAy3vwclaS4gNxk6/kIGR 2FzWXqoqf9aeAATt7GC1wQa6vTm09N3PydcPCriltAE+3Ckmi2yhroKSgADGs+mMScuo nvZO+ZgxdcIcbuD9Qgv9u7NEMtlLIK3v0omwkNljsdIeeHFv0b1eRu9i2+dbwS8GvmJl qUsw== X-Gm-Message-State: AOAM531/XJYxfbn0atTBop6LSbGFlmndMdhQzBv82Tx4kz0YB81/hXZS y9kkeRu3nAxS1NTn34ZHvRVCMw== X-Google-Smtp-Source: ABdhPJyqJD2UWpKGXVbqLCOwpvGJcWLOzlcWnB1yRcdvyrM2ucSR2PMyGQx0fSddBkTCjnJpg2lCRA== X-Received: by 2002:ac8:6b06:: with SMTP id w6mr766037qts.320.1590629740394; Wed, 27 May 2020 18:35:40 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id w43sm4404278qtw.68.2020.05.27.18.35.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 May 2020 18:35:39 -0700 (PDT) Date: Wed, 27 May 2020 21:35:39 -0400 From: Joel Fernandes To: "Paul E. McKenney" Cc: Peter Zijlstra , tglx@linutronix.de, frederic@kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, cai@lca.pw, mgorman@techsingularity.net Subject: Re: [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Message-ID: <20200528013539.GA220442@google.com> References: <20200526161057.531933155@infradead.org> <20200526161907.953304789@infradead.org> <20200527095645.GH325280@hirez.programming.kicks-ass.net> <20200527101513.GJ325303@hirez.programming.kicks-ass.net> <20200527155656.GU2869@paulmck-ThinkPad-P72> <20200527163543.GA706478@hirez.programming.kicks-ass.net> <20200527171236.GC706495@hirez.programming.kicks-ass.net> <20200527193914.GW2869@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200527193914.GW2869@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 27, 2020 at 12:39:14PM -0700, Paul E. McKenney wrote: > On Wed, May 27, 2020 at 07:12:36PM +0200, Peter Zijlstra wrote: > > On Wed, May 27, 2020 at 06:35:43PM +0200, Peter Zijlstra wrote: > > > Right, I went though them, didn't find anything obvious amiss. OK, let > > > me do a nicer patch. > > > > something like so then? > > > > --- > > Subject: rcu: Allow for smp_call_function() running callbacks from idle > > > > Current RCU hard relies on smp_call_function() callbacks running from > > interrupt context. A pending optimization is going to break that, it > > will allow idle CPUs to run the callbacks from the idle loop. This > > avoids raising the IPI on the requesting CPU and avoids handling an > > exception on the receiving CPU. > > > > Change rcu_is_cpu_rrupt_from_idle() to also accept task context, > > provided it is the idle task. > > > > Signed-off-by: Peter Zijlstra (Intel) > > Looks good to me! > > Reviewed-by: Paul E. McKenney Reviewed-by: Joel Fernandes (Google) thanks, - Joel > > > --- > > kernel/rcu/tree.c | 25 +++++++++++++++++++------ > > kernel/sched/idle.c | 4 ++++ > > 2 files changed, 23 insertions(+), 6 deletions(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index d8e9dbbefcfa..c716eadc7617 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -418,16 +418,23 @@ void rcu_momentary_dyntick_idle(void) > > EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle); > > > > /** > > - * rcu_is_cpu_rrupt_from_idle - see if interrupted from idle > > + * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle > > * > > * If the current CPU is idle and running at a first-level (not nested) > > - * interrupt from idle, return true. The caller must have at least > > - * disabled preemption. > > + * interrupt, or directly, from idle, return true. > > + * > > + * The caller must have at least disabled IRQs. > > */ > > static int rcu_is_cpu_rrupt_from_idle(void) > > { > > - /* Called only from within the scheduling-clock interrupt */ > > - lockdep_assert_in_irq(); > > + long nesting; > > + > > + /* > > + * Usually called from the tick; but also used from smp_function_call() > > + * for expedited grace periods. This latter can result in running from > > + * the idle task, instead of an actual IPI. > > + */ > > + lockdep_assert_irqs_disabled(); > > > > /* Check for counter underflows */ > > RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0, > > @@ -436,9 +443,15 @@ static int rcu_is_cpu_rrupt_from_idle(void) > > "RCU dynticks_nmi_nesting counter underflow/zero!"); > > > > /* Are we at first interrupt nesting level? */ > > - if (__this_cpu_read(rcu_data.dynticks_nmi_nesting) != 1) > > + nesting = __this_cpu_read(rcu_data.dynticks_nmi_nesting); > > + if (nesting > 1) > > return false; > > > > + /* > > + * If we're not in an interrupt, we must be in the idle task! > > + */ > > + WARN_ON_ONCE(!nesting && !is_idle_task(current)); > > + > > /* Does CPU appear to be idle from an RCU standpoint? */ > > return __this_cpu_read(rcu_data.dynticks_nesting) == 0; > > } > > diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c > > index e9cef84c2b70..05deb81bb3e3 100644 > > --- a/kernel/sched/idle.c > > +++ b/kernel/sched/idle.c > > @@ -289,6 +289,10 @@ static void do_idle(void) > > */ > > smp_mb__after_atomic(); > > > > + /* > > + * RCU relies on this call to be done outside of an RCU read-side > > + * critical section. > > + */ > > flush_smp_call_function_from_idle(); > > schedule_idle(); > >