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=-5.3 required=3.0 tests=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 5574BC3A589 for ; Thu, 15 Aug 2019 20:31:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FB972083B for ; Thu, 15 Aug 2019 20:31:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732011AbfHOUbL (ORCPT ); Thu, 15 Aug 2019 16:31:11 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38326 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730018AbfHOUbL (ORCPT ); Thu, 15 Aug 2019 16:31:11 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x7FKR1gs037549; Thu, 15 Aug 2019 16:31:09 -0400 Received: from ppma01wdc.us.ibm.com (fd.55.37a9.ip4.static.sl-reverse.com [169.55.85.253]) by mx0a-001b2d01.pphosted.com with ESMTP id 2udby9e23m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 15 Aug 2019 16:31:08 -0400 Received: from pps.filterd (ppma01wdc.us.ibm.com [127.0.0.1]) by ppma01wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x7FKRvZD019523; Thu, 15 Aug 2019 20:31:07 GMT Received: from b01cxnp22033.gho.pok.ibm.com (b01cxnp22033.gho.pok.ibm.com [9.57.198.23]) by ppma01wdc.us.ibm.com with ESMTP id 2u9nj755y9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 15 Aug 2019 20:31:07 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x7FKV7el49152490 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 15 Aug 2019 20:31:07 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 34C8BB205F; Thu, 15 Aug 2019 20:31:07 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 19067B2066; Thu, 15 Aug 2019 20:31:07 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 15 Aug 2019 20:31:07 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 0396B16C1D04; Thu, 15 Aug 2019 13:31:08 -0700 (PDT) Date: Thu, 15 Aug 2019 13:31:07 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: rcu@vger.kernel.org, frederic@kernel.org Subject: Re: need_heavy_qs flag for PREEMPT=y kernels Message-ID: <20190815203107.GL28441@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <20190811180852.GA128944@google.com> <20190811211318.GX28441@linux.ibm.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190815200432.GB23194@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-15_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908150194 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org 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. Thanx, Paul > > Still, an equal-zero comparison is probably going to be a bit cheaper than > > an equals-two comparison, and this is on the interrupt-entry fastpath, > > so this change is likely worth making. Good call!!! > > Thanks!! > > - Joel > > [snip]