From: Jens Axboe <axboe@kernel.dk>
To: Bart Van Assche <bvanassche@acm.org>,
Aaron Tomlin <atomlin@atomlin.com>,
rostedt@goodmis.org, mhiramat@kernel.org,
mathieu.desnoyers@efficios.com
Cc: johannes.thumshirn@wdc.com, kch@nvidia.com, dlemoal@kernel.org,
ritesh.list@gmail.com, loberman@redhat.com, neelx@suse.com,
sean@ashe.io, mproche@gmail.com, chjohnst@gmail.com,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] blk-mq: expose tag starvation counts via debugfs
Date: Fri, 17 Apr 2026 14:16:07 -0600 [thread overview]
Message-ID: <424110a4-4e14-4e40-af0d-59ca7a30d904@kernel.dk> (raw)
In-Reply-To: <ac8d9fd1-15c6-44cf-ba5a-85bd4aefce9b@acm.org>
On 4/17/26 12:28 PM, Bart Van Assche wrote:
> On 3/19/26 3:19 PM, Aaron Tomlin wrote:
>> To guarantee zero performance overhead for production kernels compiled
>> without debugfs, the underlying atomic_t variables and their associated
>> increment routines are strictly guarded behind CONFIG_BLK_DEBUG_FS.
>> When this configuration is disabled, the tracking logic compiles down
>> to a safe no-op.
>
> I don't think that's sufficient. Please use per-cpu counters to
> minimize the overhead for kernels in which debugfs is enabled.
Agree, this is the usual nonsense of thinking you can hide any overhead
behind a config option, when in practice production kernels very much DO
have CONFIG_DEBUGFS enabled.
--
Jens Axboe
next prev parent reply other threads:[~2026-04-17 20:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-19 22:19 [PATCH v3 0/2] blk-mq: introduce tag starvation observability Aaron Tomlin
2026-03-19 22:19 ` [PATCH v3 1/2] blk-mq: add tracepoint block_rq_tag_wait Aaron Tomlin
2026-03-19 22:19 ` [PATCH v3 2/2] blk-mq: expose tag starvation counts via debugfs Aaron Tomlin
2026-03-20 15:08 ` Laurence Oberman
2026-04-17 18:28 ` Bart Van Assche
2026-04-17 20:16 ` Jens Axboe [this message]
2026-04-18 2:29 ` Aaron Tomlin
2026-04-17 18:15 ` [PATCH v3 0/2] blk-mq: introduce tag starvation observability Aaron Tomlin
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