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=-8.4 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 BB9B2C3A59B for ; Thu, 15 Aug 2019 21:34:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 824FE20644 for ; Thu, 15 Aug 2019 21:34:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="A8W37VN6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732521AbfHOVeb (ORCPT ); Thu, 15 Aug 2019 17:34:31 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:35608 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730517AbfHOVeb (ORCPT ); Thu, 15 Aug 2019 17:34:31 -0400 Received: by mail-pg1-f196.google.com with SMTP id n4so1877186pgv.2 for ; Thu, 15 Aug 2019 14:34:30 -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=cgrTl5JdZpvmcjOSbIgnH5gT0vmwoHXYrsSlppyYY7A=; b=A8W37VN6TSshOW7zc4tsAyj8rExA7JbzubdJ8Pw5r4InjwV2VmICePZP2t8ab6tKjn 6dVuCKcYAMoyYERsownCwEj9D9GOIPnBqPzNQ9fMUsHeorGTml8h9bLvtgIFyF4vqfDJ UxYUmtka+dxxNLrXuCIehcWRnh+sx7jBSBmbc= 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=cgrTl5JdZpvmcjOSbIgnH5gT0vmwoHXYrsSlppyYY7A=; b=VJNcLcVfO/THfU34IzdV76+2KX49/Hii3xak6PJV6Y7XK7ELcgCZa3rQGQDn9hyXq8 NdK0yPwCLMHMFlyIGhmmTHekPlUgVzHAptvpA1wXHZe1czeCP4hq7xnbAiak3ViXC962 9DFI3ju1r2g9WJXUhOU2p1r4GhnyzNdF2SGxwZEq7fyVKryANhtHZrbKubrmXNNo8FeO DkngmlH20rhq7ZXk7LfU5IviRrznopimteh2xVg5LPiHqkiuifPREr6InO6eCciHWoaX ajTa+7tQeFietEfjEPokunDMs2wB7UuzvCQLmIqgbJ/45r6pDcrOM2HCnCCc5UD7pZE2 lECA== X-Gm-Message-State: APjAAAVzDNJemvq95obodMqI8+YIaj9Dy3RFgvs6YjqmiDM5nnnIMlRb 2zX5mwcTrsQ4uun/49xGtGzYiw== X-Google-Smtp-Source: APXvYqzX3RyCDpI3CetPeIPUBGA2n7pm3BdmbKZhygeVvhyijkpNo+I+cv29Wh/CkRTn6Cn3qI9HEg== X-Received: by 2002:a65:430b:: with SMTP id j11mr4960590pgq.383.1565904870105; Thu, 15 Aug 2019 14:34:30 -0700 (PDT) Received: from localhost ([172.19.216.18]) by smtp.gmail.com with ESMTPSA id m34sm2600033pje.5.2019.08.15.14.34.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Aug 2019 14:34:29 -0700 (PDT) Date: Thu, 15 Aug 2019 17:34:12 -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: <20190815213412.GB225926@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> <20190815212756.GA225926@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190815212756.GA225926@google.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 05:27:56PM -0400, Joel Fernandes 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. > > > > 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; > > Ah, I was being silly... this is already taken care off here. So you could > just drop this hunk and keep the other hunks. Sorry for the noise, to truly prevent the tick from getting turned off, I had to do something like the following, it is a complete hack but it worked well for me. I will debug this more and try to come up with a better solution tomorrow: ---8<----------------------- From: "Joel Fernandes (Google)" Subject: [PATCH] HACK: Force tick to not turn off if RCU is in urgent need of QS report Signed-off-by: Joel Fernandes (Google) --- kernel/rcu/tree.c | 12 ++++++++++++ kernel/time/tick-sched.c | 15 +++++++++++---- 2 files changed, 23 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a86c3c705e4d..60f81e151538 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -215,6 +215,18 @@ static long rcu_get_n_cbs_cpu(int cpu) return rcu_get_n_cbs_nocb_cpu(rdp); /* Works for offline, too. */ } +int rdp_nhq(void) { + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + + return !!rdp->rcu_need_heavy_qs; +} + +int rdp_uq(void) { + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + + return !!rdp->rcu_urgent_qs; +} + void rcu_softirq_qs(void) { rcu_qs(); diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index b14fc72c3b31..40df90222e34 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -851,6 +851,9 @@ static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) tick_nohz_restart(ts, now); } +int rdp_nhq(void); +int rdp_uq(void); + static void tick_nohz_full_update_tick(struct tick_sched *ts) { #ifdef CONFIG_NO_HZ_FULL @@ -862,14 +865,18 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts) if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) return; - if (can_stop_full_tick(cpu, ts)) { - trace_printk("stopping sched-tick: need_heavy_qs=%d urgent_qs=%d\n", rdp_nhq(), rdp_uq()); - trace_printk("stopping sched-tick: tick_dep_rcu=%d\n", - (atomic_read(&ts->tick_dep_mask) | TICK_DEP_MASK_RCU)); + if (can_stop_full_tick(cpu, ts) && !rdp_nhq() && !rdp_uq()) { +#if 0 + trace_printk("stopping sched-tick: need_heavy_qs=%d urgent_qs=%d\n", ); + trace_printk("stopping sched-tick: tick_dep_rcu=%d , ts %lu\n", + (atomic_read(&ts->tick_dep_mask) & TICK_DEP_MASK_RCU), (unsigned long)(&ts->tick_dep_mask)); +#endif tick_nohz_stop_sched_tick(ts, cpu); } else if (ts->tick_stopped) { +#if 0 trace_printk("restarting sched-tick\n"); +#endif tick_nohz_restart_sched_tick(ts, ktime_get()); } #endif -- 2.23.0.rc1.153.gdeed80330f-goog