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Fri, 17 Apr 2026 13:16:09 -0700 (PDT) Message-ID: <424110a4-4e14-4e40-af0d-59ca7a30d904@kernel.dk> Date: Fri, 17 Apr 2026 14:16:07 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/2] blk-mq: expose tag starvation counts via debugfs To: Bart Van Assche , Aaron Tomlin , 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 References: <20260319221956.332770-1-atomlin@atomlin.com> <20260319221956.332770-3-atomlin@atomlin.com> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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