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Mon, 04 Nov 2019 03:49:41 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xA43blSi070038; Mon, 4 Nov 2019 03:49:40 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3030.oracle.com with ESMTP id 2w1kxkm8j3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 04 Nov 2019 03:49:40 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xA43neED027567; Mon, 4 Nov 2019 03:49:40 GMT Received: from [10.159.157.81] (/10.159.157.81) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sun, 03 Nov 2019 19:49:39 -0800 Subject: Re: [PATCH 1/5] KVM: simplify branch check in host poll code To: Marcelo Tosatti Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, joao.m.martins@oracle.com, rafael.j.wysocki@intel.com, rkrcmar@redhat.com, pbonzini@redhat.com References: <1572060239-17401-1-git-send-email-zhenzhong.duan@oracle.com> <1572060239-17401-2-git-send-email-zhenzhong.duan@oracle.com> <20191101210331.GA20061@amt.cnet> From: Zhenzhong Duan Organization: Oracle Corporation Message-ID: Date: Mon, 4 Nov 2019 11:49:27 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191101210331.GA20061@amt.cnet> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9430 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1911040035 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9430 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default 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=8.0.1-1908290000 definitions=main-1911040035 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2019/11/2 5:03, Marcelo Tosatti wrote: > On Sat, Oct 26, 2019 at 11:23:55AM +0800, Zhenzhong Duan wrote: >> Remove redundant check. >> >> Signed-off-by: Zhenzhong Duan >> --- >> virt/kvm/kvm_main.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 67ef3f2..2ca2979 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -2366,13 +2366,12 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu) >> } else if (halt_poll_ns) { >> if (block_ns <= vcpu->halt_poll_ns) >> ; >> - /* we had a long block, shrink polling */ >> - else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns) >> - shrink_halt_poll_ns(vcpu); >> /* we had a short halt and our poll time is too small */ >> - else if (vcpu->halt_poll_ns < halt_poll_ns && > This is not a redundant check: it avoids from calling > into grow_halt_poll_ns, which will do: > > 1) Multiplication > 2) Cap that back to halt_poll_ns > 3) Invoke the trace_kvm_halt_poll_ns_grow tracepoint > (when in fact vcpu->halt_poll_ns did not grow). In this branch, vcpu->halt_poll_ns < block_ns is true, and if block_ns < halt_poll_ns, then vcpu->halt_poll_ns < halt_poll_ns is always true, isn't it? I realized I ignored the situation that halt_poll_ns and halt_poll_ns_grow could be updated at runtime, so pls ignore this patch, I'll fix it by following the guest haltpoll code. Thanks Zhenzhong