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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 13 Aug 2019 03:28:30 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x7D2STal23396744 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 13 Aug 2019 02:28:29 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D260CB2065; Tue, 13 Aug 2019 02:28:29 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B2F3CB2064; Tue, 13 Aug 2019 02:28:29 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.80.215.124]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 13 Aug 2019 02:28:29 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 60DF616C1109; Mon, 12 Aug 2019 19:28:29 -0700 (PDT) Date: Mon, 12 Aug 2019 19:28:29 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: rcu@vger.kernel.org Subject: Re: need_heavy_qs flag for PREEMPT=y kernels 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> <20190813010525.GB129011@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190813010525.GB129011@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 19081302-0072-0000-0000-000004522917 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011586; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01246008; UDB=6.00657500; IPR=6.01027512; MB=3.00028154; MTD=3.00000008; XFM=3.00000015; UTC=2019-08-13 02:28:31 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19081302-0073-0000-0000-00004CC33B12 Message-Id: <20190813022829.GX28441@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-12_09:,, 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-1908130025 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, Aug 12, 2019 at 09:05:25PM -0400, Joel Fernandes wrote: > On Mon, Aug 12, 2019 at 09:02:49PM -0400, Joel Fernandes wrote: > [snip] > > > Thanx, Paul > > > > > > ------------------------------------------------------------------------ > > > > > > 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())". > > Actually, the other way. if (!rcu_dynticks_curr_cpu_in_eqs()) then do the > tick_dep_set_cpu(). That does sound more likely. Still, need to work out what the breakage is. Thanx, Paul