On Sat, May 23, 2026 at 09:42:04PM -0400, Aaron Tomlin wrote:
> diff --git a/include/trace/events/block.h b/include/trace/events/block.h
> index 6aa79e2d799c..736e176f6d17 100644
> --- a/include/trace/events/block.h
> +++ b/include/trace/events/block.h
> @@ -226,6 +226,61 @@ 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 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 {
> + __entry->nr_tags = is_sched_tag ?
> + hctx->sched_tags->nr_tags :
> + hctx->tags->nr_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)
> +);
This is wrong.
If __entry->is_reserved is false, the current logic incorrectly reports the
total capacity pool depth (i.e., both reserved and standard tags combined).
I have refactored the TP_fast_assign block to evaluate the reserved status
orthogonally, ensuring nr_reserved_tags is correctly reported for I/O
schedulers. Additionally, the unreserved pool calculation has been fixed to
accurately subtract nr_reserved_tags from nr_tags.
I will include these corrections in the next iteration. Given the extent of
the functional changes to the tracepoint assignment logic, I will drop the
existing "Reviewed-by:" tags.
--
Aaron Tomlin
