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Wed, 20 Jun 2018 01:37:06 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id w5K1b5nU009976 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 20 Jun 2018 01:37:05 GMT Received: from abhmp0003.oracle.com (abhmp0003.oracle.com [141.146.116.9]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id w5K1b57n020449; Wed, 20 Jun 2018 01:37:05 GMT Received: from [10.182.69.179] (/10.182.69.179) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 19 Jun 2018 18:37:04 -0700 Subject: Re: [PATCH] blk-mq: use blk_mq_timeout_work to limit the max timeout To: Bart Van Assche , "axboe@kernel.dk" Cc: "linux-kernel@vger.kernel.org" , "linux-block@vger.kernel.org" References: <1529391610-1654-1-git-send-email-jianchao.w.wang@oracle.com> <884a5cbb5622ca5c890585a8d5dff0e3a1d60cfe.camel@wdc.com> <08b5a3e94f2265815a98abae7a8dde0894512d4e.camel@wdc.com> From: "jianchao.wang" Message-ID: Date: Wed, 20 Jun 2018 09:37:24 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <08b5a3e94f2265815a98abae7a8dde0894512d4e.camel@wdc.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8929 signatures=668702 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=8.0.1-1805220000 definitions=main-1806200015 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/20/2018 09:35 AM, Bart Van Assche wrote: > On Wed, 2018-06-20 at 09:28 +0800, jianchao.wang wrote: >> Hi Bart >> >> Thanks for your kindly response. >> >> On 06/19/2018 11:18 PM, Bart Van Assche wrote: >>> On Tue, 2018-06-19 at 15:00 +0800, Jianchao Wang wrote: >>>> blk_rq_timeout is needed to limit the max timeout value, otherwise, >>>> a idle hctx cannot be deactivated timely in shared-tag case. >>>> >>>> Fixes: 12f5b931 (blk-mq: Remove generation seqeunce) >>>> Signed-off-by: Jianchao Wang >>>> --- >>>> block/blk-mq.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/block/blk-mq.c b/block/blk-mq.c >>>> index 70c65bb..ccebe7b 100644 >>>> --- a/block/blk-mq.c >>>> +++ b/block/blk-mq.c >>>> @@ -868,7 +868,7 @@ static void blk_mq_timeout_work(struct work_struct *work) >>>> blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next); >>>> >>>> if (next != 0) { >>>> - mod_timer(&q->timeout, next); >>>> + mod_timer(&q->timeout, blk_rq_timeout(round_jiffies_up(next))); >>>> } else { >>>> /* >>>> * Request timeouts are handled as a forward rolling timer. If >>> >>> Hello Jianchao, >>> >>> What makes you think that it would be necessary to call blk_rq_timeout() from >>> blk_mq_timeout_work()? Have you noticed that blk_add_timer() already calls that >>> function? I think it is not necessary to call blk_rq_timeout() from >>> blk_mq_timeout_work() because it is guaranteed in that function that the next >>> timeout is less than BLK_MAX_TIMEOUT jiffies in the future. >>> >> >> blk_add_timer will not re-arm the timer if the timer's expire value is before the new rq's expire value. >> >> Let's look at the following scenario. >> >> 0 +30s >>> __________________|___| >> >> T0 T1 T2 >> >> T1 = T2 - 1 jiffies >> >> T0: rq_a is issued and q->timer is armed and will expire at T2 >> then rq_a is completed. >> T1: rq_b is issued and q->timer is not re-armed, because its next expire time is T2 < (T1 + 30s) >> >> T2: if rq_b have not been completed when timer expires at T2, timer would be re-armed based on the rq_b >> If we don't have blk_rq_timeout here, the next expire time is about T2 + 30s. > > Hello Jianchao, > > I disagree with the last sentence above. I think for your example blk_mq_req_expired() > will set next to T1 + 30s instead of T2 + 30s. > Would you please explain the reason ? Thanks Jianchao > Bart. > >