On Thu, Mar 19, 2026 at 06:19:54PM -0400, Aaron Tomlin wrote: > In high-performance storage environments, particularly when utilising RAID > controllers with shared tag sets (BLK_MQ_F_TAG_HCTX_SHARED), severe latency > spikes can occur when fast devices are starved of available tags. > Currently, diagnosing this specific queue contention requires deploying > dynamic kprobes or inferring sleep states, which lacks a simple, > out-of-the-box diagnostic path. > > This short series introduces dedicated, low-overhead observability for tag > exhaustion events in the block layer: > > - Patch 1 introduces the "block_rq_tag_wait" tracepoint in the tag > allocation slow-path to capture precise, event-based starvation. > > - Patch 2 complements this by exposing "wait_on_hw_tag" and > "wait_on_sched_tag" atomic counters via debugfs for quick, > point-in-time cumulative polling. > > Together, these provide storage engineers with zero-configuration > mechanisms to definitively identify shared-tag bottlenecks.
Hi Jens, Steve, Masami, Just a friendly ping on this patch. Please let me know if there is any feedback, or if you need me to make any adjustments. Kind regards, -- Aaron Tomlin
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