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 <[email protected]> >>>> --- >>>> 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. > >
