On 11/27/18 6:49 PM, Ming Lei wrote:
> On Mon, Nov 26, 2018 at 09:35:55AM -0700, Jens Axboe wrote:
>> If we are issuing a list of requests, we know if we're at the last one.
>> If we fail issuing, ensure that we call ->commits_rqs() to flush any
>> potential previous requests.
>>
>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>> ---
>> block/blk-core.c | 2 +-
>> block/blk-mq.c | 32 ++++++++++++++++++++++++--------
>> block/blk-mq.h | 2 +-
>> 3 files changed, 26 insertions(+), 10 deletions(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index c9758d185357..808a65d23f1a 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -1334,7 +1334,7 @@ blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *
>> * bypass a potential scheduler on the bottom device for
>> * insert.
>> */
>> - return blk_mq_request_issue_directly(rq);
>> + return blk_mq_request_issue_directly(rq, true);
>> }
>> EXPORT_SYMBOL_GPL(blk_insert_cloned_request);
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 6a249bf6ed00..0a12cec0b426 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -1260,6 +1260,14 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
>> if (!list_empty(list)) {
>> bool needs_restart;
>>
>> + /*
>> + * If we didn't flush the entire list, we could have told
>> + * the driver there was more coming, but that turned out to
>> + * be a lie.
>> + */
>> + if (q->mq_ops->commit_rqs)
>> + q->mq_ops->commit_rqs(hctx);
>> +
>
> Looks you miss to do it for blk_mq_do_dispatch_sched() and
> blk_mq_do_dispatch_ctx(), in which only one request is added to
> the rq_list.
blk_mq_do_dispatch() is handled through blk_mq_dispatch_rq_list(),
it doesn't need to do this on its own, it's only working on
single requests.
Ditto for blk_mq_do_dispatch()
> Maybe we can call the .commit_rqs(hctx) just at the end of
> blk_mq_sched_dispatch_requests() for cover all non-direct-issue
> cases.
I think you miss the point of ->commits_rqs() - it's only meant to
catch the case where we set bd->last == false, and never got to
the end. Like not getting a driver tag, for instance. It's not
meant to always be a kick things into gear, it's more efficient
to use bd->last for the general case, as most drivers require some
sort of locking for the submission.
--
Jens Axboe
