From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH/RFC] KVM: track pid for VCPU only on KVM_RUN ioctl Date: Tue, 19 Aug 2014 16:04:03 +0200 Message-ID: <53F35953.4000607@de.ibm.com> References: <1407249854-2953-1-git-send-email-borntraeger@de.ibm.com> <20140818050245.GA3407@kernel> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , KVM , Gleb Natapov , Rik van Riel , Raghavendra K T , Michael Mueller To: Wanpeng Li Return-path: Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:55304 "EHLO e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753309AbaHSOEP (ORCPT ); Tue, 19 Aug 2014 10:04:15 -0400 Received: from /spool/local by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 19 Aug 2014 15:04:13 +0100 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id 6DCF0219002D for ; Tue, 19 Aug 2014 15:03:52 +0100 (BST) Received: from d06av06.portsmouth.uk.ibm.com (d06av06.portsmouth.uk.ibm.com [9.149.37.217]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id s7JE49fm34406414 for ; Tue, 19 Aug 2014 14:04:09 GMT Received: from d06av06.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av06.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s7J930i2027297 for ; Tue, 19 Aug 2014 05:03:01 -0400 In-Reply-To: <20140818050245.GA3407@kernel> Sender: kvm-owner@vger.kernel.org List-ID: On 18/08/14 07:02, Wanpeng Li wrote: > Hi Christian, > On Tue, Aug 05, 2014 at 04:44:14PM +0200, Christian Borntraeger wrote: >> We currently track the pid of the task that runs the VCPU in >> vcpu_load. Since we call vcpu_load for all kind of ioctls on a >> CPU, this causes hickups due to synchronize_rcu if one CPU is >> modified by another CPU or the main thread (e.g. initialization, >> reset). We track the pid only for the purpose of yielding, so >> let's update the pid only in the KVM_RUN ioctl. >> >> In addition, don't do a synchronize_rcu on startup (pid == 0). >> >> This speeds up guest boot time on s390 noticably for some configs, e.g. >> HZ=100, no full state tracking, 64 guest cpus 32 host cpus. >> >> Signed-off-by: Christian Borntraeger >> CC: Rik van Riel >> CC: Raghavendra K T >> CC: Michael Mueller >> --- >> virt/kvm/kvm_main.c | 17 +++++++++-------- >> 1 file changed, 9 insertions(+), 8 deletions(-) >> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 9ae9135..ebc8f54 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -124,14 +124,6 @@ int vcpu_load(struct kvm_vcpu *vcpu) >> >> if (mutex_lock_killable(&vcpu->mutex)) >> return -EINTR; > > One question: > >> - if (unlikely(vcpu->pid != current->pids[PIDTYPE_PID].pid)) { > > When vcpu->pid and current->pids[PIDTYPE_PID].pid will be different? If two different thread call an ioctl on a vcpu fd. (It must be an ioctl that has done vcpu_load - almost all except for some interrupt injections)