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blk-mq: Document functions for sending request

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Add or improve documentation for function regarding creating and sending
IO requests to the hardware.

Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
André Almeida 2020-01-06 15:08:18 -03:00 committed by Jens Axboe
parent a754bd5f18
commit 105663f73e
1 changed files with 83 additions and 2 deletions
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85
block/blk-mq.c
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@ -641,6 +641,14 @@ bool blk_mq_complete_request(struct request *rq)
}
EXPORT_SYMBOL(blk_mq_complete_request);
/**
* blk_mq_start_request - Start processing a request
* @rq: Pointer to request to be started
*
* Function used by device drivers to notify the block layer that a request
* is going to be processed now, so blk layer can do proper initializations
* such as starting the timeout timer.
*/
void blk_mq_start_request(struct request *rq)
{
struct request_queue *q = rq->q;
@ -1327,6 +1335,12 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
return (queued + errors) != 0;
}
/**
* __blk_mq_run_hw_queue - Run a hardware queue.
* @hctx: Pointer to the hardware queue to run.
*
* Send pending requests to the hardware.
*/
static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
{
int srcu_idx;
@ -1424,6 +1438,15 @@ select_cpu:
return next_cpu;
}
/**
* __blk_mq_delay_run_hw_queue - Run (or schedule to run) a hardware queue.
* @hctx: Pointer to the hardware queue to run.
* @async: If we want to run the queue asynchronously.
* @msecs: Microseconds of delay to wait before running the queue.
*
* If !@async, try to run the queue now. Else, run the queue asynchronously and
* with a delay of @msecs.
*/
static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
unsigned long msecs)
{
@ -1445,12 +1468,28 @@ static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
msecs_to_jiffies(msecs));
}
/**
* blk_mq_delay_run_hw_queue - Run a hardware queue asynchronously.
* @hctx: Pointer to the hardware queue to run.
* @msecs: Microseconds of delay to wait before running the queue.
*
* Run a hardware queue asynchronously with a delay of @msecs.
*/
void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
{
__blk_mq_delay_run_hw_queue(hctx, true, msecs);
}
EXPORT_SYMBOL(blk_mq_delay_run_hw_queue);
/**
* blk_mq_run_hw_queue - Start to run a hardware queue.
* @hctx: Pointer to the hardware queue to run.
* @async: If we want to run the queue asynchronously.
*
* Check if the request queue is not in a quiesced state and if there are
* pending requests to be sent. If this is true, run the queue to send requests
* to hardware.
*/
void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
{
int srcu_idx;
@ -1474,6 +1513,11 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
}
EXPORT_SYMBOL(blk_mq_run_hw_queue);
/**
* blk_mq_run_hw_queue - Run all hardware queues in a request queue.
* @q: Pointer to the request queue to run.
* @async: If we want to run the queue asynchronously.
*/
void blk_mq_run_hw_queues(struct request_queue *q, bool async)
{
struct blk_mq_hw_ctx *hctx;
@ -1625,7 +1669,11 @@ void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
blk_mq_hctx_mark_pending(hctx, ctx);
}
/*
/**
* blk_mq_request_bypass_insert - Insert a request at dispatch list.
* @rq: Pointer to request to be inserted.
* @run_queue: If we should run the hardware queue after inserting the request.
*
* Should only be used carefully, when the caller knows we want to
* bypass a potential IO scheduler on the target device.
*/
@ -1805,6 +1853,17 @@ insert:
return BLK_STS_OK;
}
/**
* blk_mq_try_issue_directly - Try to send a request directly to device driver.
* @hctx: Pointer of the associated hardware queue.
* @rq: Pointer to request to be sent.
* @cookie: Request queue cookie.
*
* If the device has enough resources to accept a new request now, send the
* request directly to device driver. Else, insert at hctx->dispatch queue, so
* we can try send it another time in the future. Requests inserted at this
* queue have higher priority.
*/
static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
struct request *rq, blk_qc_t *cookie)
{
@ -1882,6 +1941,22 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
}
}
/**
* blk_mq_make_request - Create and send a request to block device.
* @q: Request queue pointer.
* @bio: Bio pointer.
*
* Builds up a request structure from @q and @bio and send to the device. The
* request may not be queued directly to hardware if:
* * This request can be merged with another one
* * We want to place request at plug queue for possible future merging
* * There is an IO scheduler active at this queue
*
* It will not queue the request if there is an error with the bio, or at the
* request creation.
*
* Returns: Request queue cookie.
*/
static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
{
const int is_sync = op_is_sync(bio->bi_opf);
@ -1927,7 +2002,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
plug = blk_mq_plug(q, bio);
if (unlikely(is_flush_fua)) {
/* bypass scheduler for flush rq */
/* Bypass scheduler for flush requests */
blk_insert_flush(rq);
blk_mq_run_hw_queue(data.hctx, true);
} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs ||
@ -1955,6 +2030,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
blk_add_rq_to_plug(plug, rq);
} else if (q->elevator) {
/* Insert the request at the IO scheduler queue */
blk_mq_sched_insert_request(rq, false, true, true);
} else if (plug && !blk_queue_nomerges(q)) {
/*
@ -1981,8 +2057,13 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
}
} else if ((q->nr_hw_queues > 1 && is_sync) ||
!data.hctx->dispatch_busy) {
/*
* There is no scheduler and we can try to send directly
* to the hardware.
*/
blk_mq_try_issue_directly(data.hctx, rq, &cookie);
} else {
/* Default case. */
blk_mq_sched_insert_request(rq, false, true, true);
}