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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Axel Rasmussen , Yuanchu Xie , Wei Xu , Masami Hiramatsu , Mathieu Desnoyers , "Rafael J. Wysocki" , Pavel Machek , Len Brown , Brendan Jackman , Johannes Weiner , Zi Yan , Oscar Salvador , Qi Zheng , Shakeel Butt , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [PATCH v4 0/5] mm: zone lock tracepoint instrumentation Message-Id: <20260324163918.1a3c5c960d85a4243c9ae314@linux-foundation.org> In-Reply-To: References: <20260309151317.7bba06dd@gandalf.local.home> <20260309171700.063318b5@gandalf.local.home> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: ABB4B40003 X-Stat-Signature: 8pofxstaq1eaoj1cr6r4zn3hy3nm1k3y X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1774395561-881532 X-HE-Meta: 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 T4wkj6VW b0rNUpqyNR1vKrVU6QClG8i0UFuOGsIV0Y86XKgAWFdcvODpbwaPbxCWSIuO4gUcpkUCRmMHCoqBc7F7gST2qJHhI8APSCorbvwYzibkzSnPT6k9f1HldMipH1feSSGMtkjn7dWR5PWAuDnzsjBl5CC4S86XDJjXNOb/Lei4cmBhXphFVlXbquWuSD60OfsmGQGeXQAJasWhJo4df57fGLl9e/f0IAGIvMVkkbDQfwFCz3NaGe8/wOvMUnGSqIBfN+4jWfM7sMkhocUKTJ7JPGF0Vh92bNQYrPjQbSxicp0mddV14ZHbD8q8WI2rlkgAmXfniQophvjA4JhY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 19 Mar 2026 13:22:54 +0000 Dmitry Ilvokhin wrote: > On Mon, Mar 16, 2026 at 05:40:50PM +0000, Dmitry Ilvokhin wrote: > > [...] > > > A possible generic solution is a trace_contended_release() for spin > > locks, for example: > > > > if (trace_contended_release_enabled() && > > atomic_read(&lock->val) & ~_Q_LOCKED_MASK) > > trace_contended_release(lock); > > > > This might work on x86, but could increase code size and regress > > performance on arches where spin_unlock() is inlined, such as arm64 > > under !PREEMPTION. > > I took a stab at this idea and submitted an RFC [1]. > > The implementation builds on your earlier observation from Matthew that > _raw_spin_unlock() is not inlined in most configurations. In those > cases, when the tracepoint is disabled, this adds a single NOP on the > fast path, with the conditional check staying out of line. The measured > text size increase in this configuration is +983 bytes. > > For configurations where _raw_spin_unlock() is inlined, the > instrumentation does increase code size more noticeably > (+71 KB in my measurements), since the check and out of line call is > replicated at each call site. > > This provides a generic release-side signal for contended locks, > allowing: correlation of lock holders with waiters and measurement of > contended hold times > > This RFC addressing the same visibility gap without introducing per-lock > instrumentation. > > If this tradeoff is acceptable, this could be a generic alternative to > lock-specific tracepoints. > > [1]: https://lore.kernel.org/all/51aad0415b78c5a39f2029722118fa01eac77538.1773858853.git.d@ilvokhin.com That submission has met a disappointing response. How should I proceed with this series "mm: zone lock tracepoint instrumentation"? It's not urgent so I'm inclined to put this on hold while you pursue "locking: Add contended_release tracepoint to spinning locks"? Please send that v2 sometime and hopefully Steven can help push it along?