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
--
2.7.4
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.
Bart.
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_timerout here, the next expire time is about T2 + 30s.
This is not good for sharing-tag case.
Thanks
Jianchao
>
>
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.
Bart.
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.
>
>
On 06/20/2018 09:37 AM, jianchao.wang wrote:
>
>
> 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 ?
>
Oops, yes, it is T1. I thought you were saying T0. :)
In this scenario, I have said, the T1 = T2 - 1 jiifies, it is very closed to T2.
So I said "the next expire time is about T2 + 30s"
It's my bad description.
The next time is T1 + 30s, but it is also not a good value
> Thanks
> Jianchao
>
>> Bart.
>>
>>
>