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blk-mq: add tracepoint block_rq_tag_wait #876

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blk-mq: add tracepoint block_rq_tag_wait #876

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6 changes: 6 additions & 0 deletions block/blk-mq-tag.c
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
#include <linux/kmemleak.h>

#include <linux/delay.h>
#include <trace/events/block.h>
#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-sched.h"
Expand Down Expand Up @@ -181,6 +182,11 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
if (tag != BLK_MQ_NO_TAG)
break;

/* Log the starvation event before altering task state */
trace_block_rq_tag_wait(data->q, data->hctx,
data->rq_flags & RQF_SCHED_TAGS,
data->flags);

sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE);

tag = __blk_mq_get_tag(data, bt);
Expand Down
59 changes: 59 additions & 0 deletions include/trace/events/block.h
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,65 @@ DECLARE_EVENT_CLASS(block_rq,
IOPRIO_PRIO_LEVEL(__entry->ioprio), __entry->comm)
);

/**
* block_rq_tag_wait - triggered when a request is starved of a tag
* @q: request queue of the target device
* @hctx: hardware context of the request experiencing starvation
* @is_sched_tag: indicates whether the starved pool is the software scheduler
* @alloc_flags: allocation flags dictating the specific tag pool
*
* Called immediately before the submitting context is forced to block due
* to the exhaustion of available tags (i.e., physical hardware driver
* tags, software scheduler tags, or reserved tags). This trace point
* indicates that the context will be placed into an uninterruptible state
* via sbitmap_prepare_to_wait(). If a tag is not acquired in the final
* lockless retry, the context will yield the CPU via io_schedule() until
* an active request completes and relinquishes its assigned tag.
*/
TRACE_EVENT(block_rq_tag_wait,

TP_PROTO(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
bool is_sched_tag, unsigned int alloc_flags),

TP_ARGS(q, hctx, is_sched_tag, alloc_flags),

TP_STRUCT__entry(
__field( dev_t, dev )
__field( u32, hctx_id )
__field( u32, nr_tags )
__field( bool, is_sched_tag )
__field( bool, is_reserved )
),

TP_fast_assign(
__entry->dev = q->disk ? disk_devt(q->disk) : 0;
__entry->hctx_id = hctx->queue_num;
__entry->is_sched_tag = is_sched_tag;
__entry->is_reserved = alloc_flags & BLK_MQ_REQ_RESERVED;

if (__entry->is_reserved) {
__entry->nr_tags = is_sched_tag ?
hctx->sched_tags->nr_reserved_tags :
hctx->tags->nr_reserved_tags;
} else {
if (is_sched_tag)
__entry->nr_tags = hctx->sched_tags->nr_tags -
hctx->sched_tags->nr_reserved_tags;
else
__entry->nr_tags = hctx->tags->nr_tags -
hctx->tags->nr_reserved_tags;
}

),

TP_printk("%d,%d hctx=%u starved on %s%s tags (depth=%u)",
MAJOR(__entry->dev), MINOR(__entry->dev),
__entry->hctx_id,
__entry->is_sched_tag ? "scheduler" : "hardware",
__entry->is_reserved ? " reserved" : "",
__entry->nr_tags)
);

/**
* block_rq_insert - insert block operation request into queue
* @rq: block IO operation request
Expand Down