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=-5.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, 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 6D4E8C3A589 for ; Fri, 16 Aug 2019 00:02:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 330C12086C for ; Fri, 16 Aug 2019 00:02:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="awKTJsFI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726119AbfHPACU (ORCPT ); Thu, 15 Aug 2019 20:02:20 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:34913 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725978AbfHPACU (ORCPT ); Thu, 15 Aug 2019 20:02:20 -0400 Received: by mail-pf1-f194.google.com with SMTP id d85so2162231pfd.2 for ; Thu, 15 Aug 2019 17:02:20 -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=bBMO+81b+9FqbnypyztdBrioxofnj72xFOfPW1A0L4M=; b=awKTJsFIk4r/ROTIGzOjLkvhueBvIJr27EXtiZYutXqjH0+7j/l+3hT1i/TWM5ptu7 fOkqmOjHvk2wCwGUBCl4ZX+sbBgqQIK2Ozye6iO7RnWJarcZ8JpuLUsEjmpHt5lbck/j kFFZXt/Ky6OO1an6EjvINW4JjK2OiPzqQUEqo= 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=bBMO+81b+9FqbnypyztdBrioxofnj72xFOfPW1A0L4M=; b=e37z2iCTLQ+nfFdZaKiVHwOM/dyvZ21GJdUtAMyEn6ClxlBOFvT1M2OEdGSfSf2eF+ UFiuNSX+t4k4ZjFdayZZPbtAQ9wrRby4kfKhBk9g+gecPoJZaBs+e2wSTSg4OG5NVWFh JaFdqqHM2FW0n/Qmdu1IbNuFAva6IysXNFk8TteymlmWAbDZfGqgzmv0KP5eOGPRwFcz PhiyP62+p/zLLUoCaEnk3JpmCCc+lTPz2MfvfCUH0+WY4EOvFZ8gom0gg2USiZE/Pvq9 CasYT6aRHg+f7HaO4PY2+tR3mOm1PCHamgY+0g67VSPb/1kaReKR90oW1JauZnll69Wb NV4w== X-Gm-Message-State: APjAAAUZxc08huzsU7LjCx1zaUvWs9gIrr4NMBUlFv8OUaDWo18kI10q y+ncb/iotrv9zPyhuNfxFfUBxg== X-Google-Smtp-Source: APXvYqyEO0qasvzudUDiB8xMlvl9LOmKD81rA/XDNjXZWwGNbgksxvJ2qS04IsA48oRkKelK/v5NOQ== X-Received: by 2002:a65:4205:: with SMTP id c5mr5335831pgq.265.1565913739568; Thu, 15 Aug 2019 17:02:19 -0700 (PDT) Received: from localhost ([172.19.216.18]) by smtp.gmail.com with ESMTPSA id x2sm2987789pja.22.2019.08.15.17.02.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Aug 2019 17:02:18 -0700 (PDT) Date: Thu, 15 Aug 2019 20:02:01 -0400 From: Joel Fernandes To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, frederic@kernel.org Subject: Re: need_heavy_qs flag for PREEMPT=y kernels Message-ID: <20190816000201.GC225926@google.com> References: <20190812032142.GA171001@google.com> <20190812035306.GE28441@linux.ibm.com> <20190812212013.GB48751@google.com> <20190812230138.GS28441@linux.ibm.com> <20190813010249.GA129011@google.com> <20190815171714.GA1023@linux.ibm.com> <20190815200432.GB23194@google.com> <20190815203107.GL28441@linux.ibm.com> <20190815212216.GA224191@google.com> <20190815214542.GM28441@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190815214542.GM28441@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 Thu, Aug 15, 2019 at 02:45:42PM -0700, Paul E. McKenney wrote: > On Thu, Aug 15, 2019 at 05:22:16PM -0400, Joel Fernandes wrote: > > On Thu, Aug 15, 2019 at 01:31:07PM -0700, Paul E. McKenney wrote: > > > On Thu, Aug 15, 2019 at 04:04:32PM -0400, Joel Fernandes wrote: > > > > On Thu, Aug 15, 2019 at 10:17:14AM -0700, Paul E. McKenney wrote: > > > > > On Mon, Aug 12, 2019 at 09:02:49PM -0400, Joel Fernandes wrote: > > > > > > On Mon, Aug 12, 2019 at 04:01:38PM -0700, Paul E. McKenney wrote: > > > > > > > > > > [ . . . ] > > > > > > > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > > > > > index 8c494a692728..ad906d6a74fb 100644 > > > > > > > --- a/kernel/rcu/tree.c > > > > > > > +++ b/kernel/rcu/tree.c > > > > > > > @@ -651,6 +651,12 @@ static __always_inline void rcu_nmi_exit_common(bool irq) > > > > > > > */ > > > > > > > if (rdp->dynticks_nmi_nesting != 1) { > > > > > > > trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks); > > > > > > > + if (tick_nohz_full_cpu(rdp->cpu) && > > > > > > > + rdp->dynticks_nmi_nesting == 2 && > > > > > > > + rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { > > > > > > > + rdp->rcu_forced_tick = true; > > > > > > > + tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU); > > > > > > > + } > > > > > > > > > > > > > > > > > > Instead of checking dynticks_nmi_nesting == 2 in rcu_nmi_exit_common(), can > > > > > > we do the tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU) from > > > > > > rcu_nmi_enter_common() ? We could add this code there, under the "if > > > > > > (rcu_dynticks_curr_cpu_in_eqs())". > > > > > > > > > > This would need to go in an "else" clause, correct? But there would still > > > > > want to be a check for interrupt from base level (which would admittedly > > > > > be an equality comparison with zero) and we would also still need to check > > > > > for rdp->rcu_urgent_qs && !rdp->rcu_forced_tick. > > > > > > > > True, agreed. I replied to this before saying it should be > > > > !rcu_dynticks_curr_cpu_in_eqs() in the "if" ;) But it seems I could also be > > > > missing the check for TICK_DEP_MASK_RCU in my tree so I think we need this as > > > > well which is below as diff. Testing it more now! > > > > > > > > And, with this I do get many more ticks during the test. But there are > > > > intervals where the tick is not seen. Still it is much better than before: > > > > > > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > > > index be9707f68024..e697c7a2ce67 100644 > > > > --- a/kernel/time/tick-sched.c > > > > +++ b/kernel/time/tick-sched.c > > > > @@ -198,6 +198,10 @@ static bool check_tick_dependency(atomic_t *dep) > > > > return true; > > > > } > > > > > > > > + if (val & TICK_DEP_MASK_CLOCK_RCU) { > > > > + return true; > > > > + } > > > > + > > > > return false; > > > > } > > > > > > That one is not in my tree, either. Frederic, should I add this to > > > your patch? For that matter, may I add your Signed-off-by as well? > > > Your original is in my -rcu tree at: > > > > > > 0cb41806c799 ("EXP nohz: Add TICK_DEP_BIT_RCU") > > > > > > I am testing Joel's suggested addition now. > > > > Actually there's more addition needed! I found another thing missing: > > > > There's a per-cpu &tick_dep_mask and a per-cpu ts->tick_dep_mask. It seems > > RCU is setting the latter. > > As I understand it, tick_dep_mask forces the tick on globally, > ts->tick_dep_mask forces it on for a specific CPU (which RCU uses when it > needs a quiescent state from that CPU), current->tick_dep_mask forces > it on for a specific task (which RCU uses for callback invocation > and certain rcutorture kthreads), and I don't pretend to understand > current->signal->tick_dep_mask (the comment says something about POSIX > CPU timers). Right. I am pretty new to all of these so I could have something incorrect in a hurry. But thanks for the explanation of your understanding of these. Yes this commit talks about timers as well for the signal->tick_dep_mask: d027d45d8a17 ("nohz: New tick dependency mask") > But it looks to me that can_stop_full_tick() and check_tick_dependency() > already cover all of these. What am I missing? As you mentioned, all of these are covered. > > So I added a check for both, below is the diff: > > > > However, I see in some cases that the tick_dep_mask is just 0 but I have to > > debug that tomorrow if that's an issue on the RCU side of things. For now, > > below should be the completed Frederick patch which you could squash into his > > if he's Ok with it: > > > > ---8<----------------------- > > > > diff --git a/include/linux/tick.h b/include/linux/tick.h > > index f92a10b5e112..3f476e2a4bf7 100644 > > --- a/include/linux/tick.h > > +++ b/include/linux/tick.h > > @@ -108,7 +108,8 @@ enum tick_dep_bits { > > TICK_DEP_BIT_POSIX_TIMER = 0, > > TICK_DEP_BIT_PERF_EVENTS = 1, > > TICK_DEP_BIT_SCHED = 2, > > - TICK_DEP_BIT_CLOCK_UNSTABLE = 3 > > + TICK_DEP_BIT_CLOCK_UNSTABLE = 3, > > + TICK_DEP_BIT_RCU = 4 > > }; > > > > #define TICK_DEP_MASK_NONE 0 > > @@ -116,6 +117,7 @@ enum tick_dep_bits { > > #define TICK_DEP_MASK_PERF_EVENTS (1 << TICK_DEP_BIT_PERF_EVENTS) > > #define TICK_DEP_MASK_SCHED (1 << TICK_DEP_BIT_SCHED) > > #define TICK_DEP_MASK_CLOCK_UNSTABLE (1 << TICK_DEP_BIT_CLOCK_UNSTABLE) > > +#define TICK_DEP_MASK_RCU (1 << TICK_DEP_BIT_RCU) > > > > #ifdef CONFIG_NO_HZ_COMMON > > extern bool tick_nohz_enabled; > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index be9707f68024..a613916cc3f0 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > @@ -198,6 +198,11 @@ static bool check_tick_dependency(atomic_t *dep) > > return true; > > } > > > > + if (val & TICK_DEP_MASK_RCU) { > > + trace_tick_stop(0, TICK_DEP_MASK_RCU); > > + return true; > > + } > > + > > return false; > > } > > > > @@ -208,8 +213,13 @@ static bool can_stop_full_tick(int cpu, struct tick_sched *ts) > > if (unlikely(!cpu_online(cpu))) > > return false; > > > > - if (check_tick_dependency(&tick_dep_mask)) > > + if (check_tick_dependency(&ts->tick_dep_mask)) { > > return false; > > + } > > + > > + if (check_tick_dependency(&tick_dep_mask)) { > > + return false; > > + } > > > > if (check_tick_dependency(&ts->tick_dep_mask)) > > return false; > > You lost me on this one. How does it help to check ts->tick_dep_mask > twice? And why is it important to check it before checking tick_dep_mask, > especially given that the common case of all-zero masks will cause > all to be checked anyway? You are right. In a later reply I had mentioned to you to drop this hunk. It is not needed. I will pull your -rcu dev branch now to get the latest and will test the RCU dyntick code to see if I can make that work with the tick-sched code. Keep you posted! thanks, - Joel