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Mon, 04 Nov 2019 03:10:53 +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 xA4343Cr017272; Mon, 4 Nov 2019 03:10:53 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3030.oracle.com with ESMTP id 2w1kxkjwn1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 04 Nov 2019 03:10:53 +0000 Received: from abhmp0008.oracle.com (abhmp0008.oracle.com [141.146.116.14]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id xA43ApKq017345; Mon, 4 Nov 2019 03:10:51 GMT Received: from [192.168.0.4] (/111.206.84.95) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 04 Nov 2019 03:10:50 +0000 Subject: Re: [PATCH 5/5] cpuidle-haltpoll: fix up the branch check 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> <1572060239-17401-6-git-send-email-zhenzhong.duan@oracle.com> <20191101212613.GB20672@amt.cnet> From: Zhenzhong Duan Organization: Oracle Corporation Message-ID: Date: Mon, 4 Nov 2019 11:10:25 +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: <20191101212613.GB20672@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-1911040031 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-1911040032 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2019/11/2 5:26, Marcelo Tosatti wrote: > On Sat, Oct 26, 2019 at 11:23:59AM +0800, Zhenzhong Duan wrote: >> Ensure pool time is longer than block_ns, so there is a margin to >> avoid vCPU get into block state unnecessorily. >> >> Signed-off-by: Zhenzhong Duan >> --- >> drivers/cpuidle/governors/haltpoll.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/cpuidle/governors/haltpoll.c b/drivers/cpuidle/governors/haltpoll.c >> index 4b00d7a..59eadaf 100644 >> --- a/drivers/cpuidle/governors/haltpoll.c >> +++ b/drivers/cpuidle/governors/haltpoll.c >> @@ -81,9 +81,9 @@ static void adjust_poll_limit(struct cpuidle_device *dev, unsigned int block_us) >> u64 block_ns = block_us*NSEC_PER_USEC; >> >> /* Grow cpu_halt_poll_us if >> - * cpu_halt_poll_us < block_ns < guest_halt_poll_us >> + * cpu_halt_poll_us <= block_ns < guest_halt_poll_us >> */ >> - if (block_ns > dev->poll_limit_ns && block_ns <= guest_halt_poll_ns) { >> + if (block_ns >= dev->poll_limit_ns && block_ns < guest_halt_poll_ns) { > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > If block_ns == guest_halt_poll_ns, you won't allow dev->poll_limit_ns to > grow. Why is that? Maybe I'm too strict here. My understanding is: if block_ns = guest_halt_poll_ns, dev->poll_limit_ns will grow to guest_halt_poll_ns, then block_ns = dev->poll_limit_ns, there is not a margin to ensure poll time is enough to cover the equal block time. In this case, shrinking may be a better choice? > >> @@ -101,7 +101,7 @@ static void adjust_poll_limit(struct cpuidle_device *dev, unsigned int block_us) >> val = guest_halt_poll_ns; >> >> dev->poll_limit_ns = val; >> - } else if (block_ns > guest_halt_poll_ns && >> + } else if (block_ns >= guest_halt_poll_ns && >> guest_halt_poll_allow_shrink) { >> unsigned int shrink = guest_halt_poll_shrink; > And here you shrink if block_ns == guest_halt_poll_ns. Not sure > why that makes sense either. See above explanation. Zhenzhong