From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753101AbcGFKGU (ORCPT ); Wed, 6 Jul 2016 06:06:20 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:37681 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751622AbcGFKGR (ORCPT ); Wed, 6 Jul 2016 06:06:17 -0400 X-IBM-Helo: d23dlp01.au.ibm.com X-IBM-MailFrom: xinhui.pan@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org;linux-s390@vger.kernel.org Date: Wed, 06 Jul 2016 18:05:58 +0800 From: xinhui User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.8.0 MIME-Version: 1.0 To: Peter Zijlstra CC: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-s390@vger.kernel.org, mingo@redhat.com, mpe@ellerman.id.au, paulus@samba.org, benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com, waiman.long@hpe.com, will.deacon@arm.com, boqun.feng@gmail.com, dave@stgolabs.net, schwidefsky@de.ibm.com, pbonzini@redhat.com Subject: Re: [PATCH v2 0/4] implement vcpu preempted check References: <1467124991-13164-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160706065255.GH30909@twins.programming.kicks-ass.net> In-Reply-To: <20160706065255.GH30909@twins.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16070610-0040-0000-0000-000001BDA187 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16070610-0041-0000-0000-00000A05C59D Message-Id: <577CD806.8000008@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-07-06_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1607060090 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016年07月06日 14:52, Peter Zijlstra wrote: > On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote: >> change fomr v1: >> a simplier definition of default vcpu_is_preempted >> skip mahcine type check on ppc, and add config. remove dedicated macro. >> add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. >> add more comments >> thanks boqun and Peter's suggestion. >> >> This patch set aims to fix lock holder preemption issues. >> >> test-case: >> perf record -a perf bench sched messaging -g 400 -p && perf report >> >> 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock >> 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner >> 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock >> 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task >> 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq >> 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is >> 2.49% sched-messaging [kernel.vmlinux] [k] system_call >> >> We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin >> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner. >> These spin_on_onwer variant also cause rcu stall before we apply this patch set >> > > Paolo, could you help out with an (x86) KVM interface for this? > > Waiman, could you see if you can utilize this to get rid of the > SPIN_THRESHOLD in qspinlock_paravirt? > hmm. maybe something like below. wait_node can go into pv_wait() earlier as soon as the prev cpu is preempted. but for the wait_head, as qspinlock does not record the lock_holder correctly(thanks to lock stealing), vcpu preemption check might get wrong results. Waiman, I have used one hash table to keep the lock holder in my ppc implementation patch. I think we could do something similar in generic code? diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 74c4a86..40560e8 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -312,7 +312,8 @@ pv_wait_early(struct pv_node *prev, int loop) if ((loop & PV_PREV_CHECK_MASK) != 0) return false; - return READ_ONCE(prev->state) != vcpu_running; + return READ_ONCE(prev->state) != vcpu_running || + vcpu_is_preempted(prev->cpu); } /*