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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 23 Jul 2018 08:22:29 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w6NCMSDL17301856 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 23 Jul 2018 12:22:28 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9E2F8B205F; Mon, 23 Jul 2018 08:22:12 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7E183B2066; Mon, 23 Jul 2018 08:22:12 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.80.230.11]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 23 Jul 2018 08:22:12 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 09C7716C2400; Mon, 23 Jul 2018 05:22:31 -0700 (PDT) Date: Mon, 23 Jul 2018 05:22:31 -0700 From: "Paul E. McKenney" To: David Woodhouse Cc: Christian Borntraeger , Peter Zijlstra , mhillenb@amazon.de, linux-kernel , kvm Subject: Re: [RFC] Make need_resched() return true when rcu_urgent_qs requested Reply-To: paulmck@linux.vnet.ibm.com References: <20180712125351.GP3593@linux.vnet.ibm.com> <20180712161704.GA20726@linux.vnet.ibm.com> <20180716154015.GA21419@linux.vnet.ibm.com> <1531815548.19223.23.camel@infradead.org> <20180717125653.GH12945@linux.vnet.ibm.com> <20180718153628.GA24359@linux.vnet.ibm.com> <1531929711.3414.29.camel@infradead.org> <20180718163712.GB12945@linux.vnet.ibm.com> <20180719170953.GA17730@linux.vnet.ibm.com> <1532333339.14652.12.camel@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1532333339.14652.12.camel@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18072312-0052-0000-0000-000003125067 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009417; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01064952; UDB=6.00547007; IPR=6.00842809; MB=3.00022278; MTD=3.00000008; XFM=3.00000015; UTC=2018-07-23 12:22:31 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18072312-0053-0000-0000-00005D767508 Message-Id: <20180723122230.GM12945@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-07-23_02:,, 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=550 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1807230145 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 23, 2018 at 10:08:59AM +0200, David Woodhouse wrote: > On Thu, 2018-07-19 at 10:09 -0700, Paul E. McKenney wrote: > > > > Of course, the real reason for the lack of fault on your part will not > > because I believe I found the bug elsewhere, but instead because I will > > be dropping your patch (and mine as well) on Frederic's advice.  ;-) > > You're keeping the need_resched() one though? Yes. This the current commit in -rcu (which will change when I rebase onto v4.19-rc1, if not earlier): fcf0407e6e63 ("rcu: Make need_resched() respond to urgent RCU-QS needs") > And we are still left with the fact that CONTEXT_TRACKING_FORCE is > making the existing code in guest_enter_irqoff() do the wrong thing for > !NO_HZ_FULL. But in fact the rcu_virt_note_context_switch() there is > completely redundant now we fixed need_resched(), so can be dropped, > leaving only the rcu_user_enter/exit calls for the NO_HZ_FULL case? I am not yet convinced that we know exactly the right thing to be doing for guest OSes for either value of NO_HZ_FULL, much less that we are actually doing it. ;-) But what does your testing say? Thanx, Paul