Re: [PATCH] io-controller: Preempt a non-rt queue if a rt ioq is present in ancestor or sibling groups

Gui Jianfeng
2009-06-23T06:46:23Z

Vivek Goyal wrote:
> On Mon, Jun 22, 2009 at 03:44:08PM +0800, Gui Jianfeng wrote:
>> Preempt the ongoing non-rt ioq if there are rt ioqs waiting for dispatching
>> in ancestor or sibling groups. It will give other group's rt ioq an chance
>> to dispatch ASAP.
>>
>
> Hi Gui,
>
> Will new preempton logic of traversing up the hiearchy so that both new
> queue and old queue are at same level to take a preemption decision not
> take care of above scenario?

Hi Vivek,

Would you explain a bit what do you mean about "both new queue and old queue
are at same level to take a preemption decision". I don't understand it well.

>
> Please have a look at bfq_find_matching_entity().
>
> At the same time we probably don't want to preempt the non-rt queue
> with an RT queue in sibling group until and unless sibling group is an
> RT group.
>
> root
> / \
> BEgrpA BEgrpB
> | |
> BEioq1 RTioq2
>
> Above we got two BE group A and B and assume ioq in group A is being
> served and then an RT request in group B comes. Because group B is an
> BE class group, we should not preempt the queue in group A.

Yes, i also have this concern. So, it does not allow non-rt group preempts
another group. I'll check whether there is a way to address this issue.

>
> Thanks
> Vivek
>
>
>> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
>> ---
>> block/elevator-fq.c | 44 +++++++++++++++++++++++++++++++++++++++-----
>> block/elevator-fq.h | 1 +
>> 2 files changed, 40 insertions(+), 5 deletions(-)
>>
>> diff --git a/block/elevator-fq.c b/block/elevator-fq.c
>> index 2ad40eb..80526fd 100644
>> --- a/block/elevator-fq.c
>> +++ b/block/elevator-fq.c
>> @@ -3245,8 +3245,16 @@ void elv_add_ioq_busy(struct elv_fq_data *efqd, struct io_queue *ioq)
>> elv_mark_ioq_busy(ioq);
>> efqd->busy_queues++;
>> if (elv_ioq_class_rt(ioq)) {
>> + struct io_entity *entity;
>> struct io_group *iog = ioq_to_io_group(ioq);
>> +
>> iog->busy_rt_queues++;
>> + entity = iog->entity.parent;
>> +
>> + for_each_entity(entity) {
>> + iog = io_entity_to_iog(entity);
>> + iog->sub_busy_rt_queues++;
>> + }
>> }
>>
>> #ifdef CONFIG_DEBUG_GROUP_IOSCHED
>> @@ -3290,9 +3298,18 @@ void elv_del_ioq_busy(struct elevator_queue *e, struct io_queue *ioq,
>> elv_clear_ioq_busy(ioq);
>> BUG_ON(efqd->busy_queues == 0);
>> efqd->busy_queues--;
>> +
>> if (elv_ioq_class_rt(ioq)) {
>> + struct io_entity *entity;
>> struct io_group *iog = ioq_to_io_group(ioq);
>> +
>> iog->busy_rt_queues--;
>> + entity = iog->entity.parent;
>> +
>> + for_each_entity(entity) {
>> + iog = io_entity_to_iog(entity);
>> + iog->sub_busy_rt_queues--;
>> + }
>> }
>>
>> elv_deactivate_ioq(efqd, ioq, requeue);
>> @@ -3735,12 +3752,32 @@ int elv_iosched_expire_ioq(struct request_queue *q, int slice_expired,
>> return ret;
>> }
>>
>> +static int check_rt_queue(struct io_queue *ioq)
>> +{
>> + struct io_group *iog;
>> + struct io_entity *entity;
>> +
>> + iog = ioq_to_io_group(ioq);
>> +
>> + if (iog->busy_rt_queues)
>> + return 1;
>> +
>> + entity = iog->entity.parent;
>> +
>> + for_each_entity(entity) {
>> + iog = io_entity_to_iog(entity);
>> + if (iog->sub_busy_rt_queues)
>> + return 1;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> /* Common layer function to select the next queue to dispatch from */
>> void *elv_fq_select_ioq(struct request_queue *q, int force)
>> {
>> struct elv_fq_data *efqd = &q->elevator->efqd;
>> struct io_queue *new_ioq = NULL, *ioq = elv_active_ioq(q->elevator);
>> - struct io_group *iog;
>> int slice_expired = 1;
>>
>> if (!elv_nr_busy_ioq(q->elevator))
>> @@ -3811,12 +3848,9 @@ void *elv_fq_select_ioq(struct request_queue *q, int force)
>> /*
>> * If we have a RT cfqq waiting, then we pre-empt the current non-rt
>> * cfqq.
>> - *
>> - * TODO: This does not seem right across the io groups. Fix it.
>> */
>> - iog = ioq_to_io_group(ioq);
>>
>> - if (!elv_ioq_class_rt(ioq) && iog->busy_rt_queues) {
>> + if (!elv_ioq_class_rt(ioq) && check_rt_queue(ioq)) {
>> /*
>> * We simulate this as cfqq timed out so that it gets to bank
>> * the remaining of its time slice.
>> diff --git a/block/elevator-fq.h b/block/elevator-fq.h
>> index b3193f8..be6c1af 100644
>> --- a/block/elevator-fq.h
>> +++ b/block/elevator-fq.h
>> @@ -248,6 +248,7 @@ struct io_group {
>> * non-RT cfqq in service when this value is non-zero.
>> */
>> unsigned int busy_rt_queues;
>> + unsigned int sub_busy_rt_queues;
>>
>> int deleting;
>> unsigned short iocg_id;
>> --
>> 1.5.4.rc3
>>
>
>
>

--
Regards
Gui Jianfeng