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[73.143.21.186]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8cfc9088df1sm843364185a.25.2026.03.23.09.00.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Mar 2026 09:00:56 -0700 (PDT) From: "Vineeth Pillai (Google)" To: Steven Rostedt , Peter Zijlstra , Dmitry Ilvokhin Cc: "Vineeth Pillai (Google)" , Masami Hiramatsu , Mathieu Desnoyers , Ingo Molnar , Jens Axboe , io-uring@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexei Starovoitov , Daniel Borkmann , Marcelo Ricardo Leitner , Xin Long , Jon Maloy , Aaron Conole , Eelco Chaudron , Ilya Maximets , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-sctp@vger.kernel.org, tipc-discussion@lists.sourceforge.net, dev@openvswitch.org, Jiri Pirko , Oded Gabbay , Koby Elbaz , dri-devel@lists.freedesktop.org, "Rafael J. Wysocki" , Viresh Kumar , "Gautham R. Shenoy" , Huang Rui , Mario Limonciello , Len Brown , Srinivas Pandruvada , linux-pm@vger.kernel.org, MyungJoo Ham , Kyungmin Park , Chanwoo Choi , =?UTF-8?q?Christian=20K=C3=B6nig?= , Sumit Semwal , linaro-mm-sig@lists.linaro.org, Eddie James , Andrew Jeffery , Joel Stanley , linux-fsi@lists.ozlabs.org, David Airlie , Simona Vetter , Alex Deucher , Danilo Krummrich , Matthew Brost , Philipp Stanner , Harry Wentland , Leo Li , amd-gfx@lists.freedesktop.org, Jiri Kosina , Benjamin Tissoires , linux-input@vger.kernel.org, Wolfram Sang , linux-i2c@vger.kernel.org, Mark Brown , Michael Hennerich , =?UTF-8?q?Nuno=20S=C3=A1?= , linux-spi@vger.kernel.org, "James E.J. Bottomley" , "Martin K. Petersen" , linux-scsi@vger.kernel.org, Chris Mason , David Sterba , linux-btrfs@vger.kernel.org, Thomas Gleixner , Andrew Morton , SeongJae Park , linux-mm@kvack.org, Borislav Petkov , Dave Hansen , x86@kernel.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 00/19] tracepoint: Avoid double static_branch evaluation at guarded call sites Date: Mon, 23 Mar 2026 12:00:19 -0400 Message-ID: <20260323160052.17528-1-vineeth@bitbyteword.org> X-Mailer: git-send-email 2.53.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" When a caller already guards a tracepoint with an explicit enabled check: if (trace_foo_enabled() && cond) trace_foo(args); trace_foo() internally re-evaluates the static_branch_unlikely() key. Since static branches are patched binary instructions the compiler cannot fold the two evaluations, so every such site pays the cost twice. This series introduces trace_call__##name() as a companion to trace_##name(). It calls __do_trace_##name() directly, bypassing the redundant static-branch re-check, while preserving all other correctness properties of the normal path (RCU-watching assertion, might_fault() for syscall tracepoints). The internal __do_trace_##name() symbol is not leaked to call sites; trace_call__##name() is the only new public API. if (trace_foo_enabled() && cond) trace_call__foo(args); /* calls __do_trace_foo() directly */ The first patch adds the three-location change to include/linux/tracepoint.h (__DECLARE_TRACE, __DECLARE_TRACE_SYSCALL, and the !TRACEPOINTS_ENABLED stub). The remaining 18 patches mechanically convert all guarded call sites found in the tree: kernel/, io_uring/, net/, accel/habanalabs, cpufreq/, devfreq/, dma-buf/, fsi/, drm/, HID, i2c/, spi/, scsi/ufs/, btrfs/, net/devlink/, kernel/time/, kernel/trace/, mm/damon/, and arch/x86/. This series is motivated by Peter Zijlstra's observation in the discussion around Dmitry Ilvokhin's locking tracepoint instrumentation series, where he noted that compilers cannot optimize static branches and that guarded call sites end up evaluating the static branch twice for no reason, and by Steven Rostedt's suggestion to add a proper API instead of exposing internal implementation details like __do_trace_##name() directly to call sites: https://lore.kernel.org/linux-trace-kernel/8298e098d3418cb446ef396f119edac58a3414e9.1772642407.git.d@ilvokhin.com Suggested-by: Steven Rostedt Suggested-by: Peter Zijlstra Changes in v2: - Renamed trace_invoke_##name() to trace_call__##name() (double underscore) per review comments. - Added 4 new patches covering sites missed in v1, found using coccinelle to scan the tree (Keith Busch): * net/devlink: guarded tracepoint_enabled() block in trap.c * kernel/time: early-return guard in tick-sched.c (tick_stop) * kernel/trace: early-return guard in trace_benchmark.c * mm/damon: early-return guard in core.c * arch/x86: do_trace_*() wrapper functions in lib/msr.c, which are called exclusively from tracepoint_enabled()-guarded sites in asm/msr.h v1: https://lore.kernel.org/linux-trace-kernel/abSqrJ1J59RQC47U@kbusch-mbp/ Vineeth Pillai (Google) (19): tracepoint: Add trace_call__##name() API kernel: Use trace_call__##name() at guarded tracepoint call sites io_uring: Use trace_call__##name() at guarded tracepoint call sites net: Use trace_call__##name() at guarded tracepoint call sites accel/habanalabs: Use trace_call__##name() at guarded tracepoint call sites cpufreq: Use trace_call__##name() at guarded tracepoint call sites devfreq: Use trace_call__##name() at guarded tracepoint call sites dma-buf: Use trace_call__##name() at guarded tracepoint call sites fsi: Use trace_call__##name() at guarded tracepoint call sites drm: Use trace_call__##name() at guarded tracepoint call sites HID: Use trace_call__##name() at guarded tracepoint call sites i2c: Use trace_call__##name() at guarded tracepoint call sites spi: Use trace_call__##name() at guarded tracepoint call sites scsi: ufs: Use trace_call__##name() at guarded tracepoint call sites btrfs: Use trace_call__##name() at guarded tracepoint call sites net: devlink: Use trace_call__##name() at guarded tracepoint call sites kernel: time, trace: Use trace_call__##name() at guarded tracepoint call sites mm: damon: Use trace_call__##name() at guarded tracepoint call sites x86: msr: Use trace_call__##name() at guarded tracepoint call sites arch/x86/lib/msr.c | 6 +++--- drivers/accel/habanalabs/common/device.c | 12 ++++++------ drivers/accel/habanalabs/common/mmu/mmu.c | 3 ++- drivers/accel/habanalabs/common/pci/pci.c | 4 ++-- drivers/cpufreq/amd-pstate.c | 10 +++++----- drivers/cpufreq/cpufreq.c | 2 +- drivers/cpufreq/intel_pstate.c | 2 +- drivers/devfreq/devfreq.c | 2 +- drivers/dma-buf/dma-fence.c | 4 ++-- drivers/fsi/fsi-master-aspeed.c | 2 +- drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 2 +- drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 4 ++-- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +- drivers/gpu/drm/scheduler/sched_entity.c | 4 ++-- drivers/hid/intel-ish-hid/ipc/pci-ish.c | 2 +- drivers/i2c/i2c-core-slave.c | 2 +- drivers/spi/spi-axi-spi-engine.c | 4 ++-- drivers/ufs/core/ufshcd.c | 12 ++++++------ fs/btrfs/extent_map.c | 4 ++-- fs/btrfs/raid56.c | 4 ++-- include/linux/tracepoint.h | 11 +++++++++++ io_uring/io_uring.h | 2 +- kernel/irq_work.c | 2 +- kernel/sched/ext.c | 2 +- kernel/smp.c | 2 +- kernel/time/tick-sched.c | 12 ++++++------ kernel/trace/trace_benchmark.c | 2 +- mm/damon/core.c | 2 +- net/core/dev.c | 2 +- net/core/xdp.c | 2 +- net/devlink/trap.c | 2 +- net/openvswitch/actions.c | 2 +- net/openvswitch/datapath.c | 2 +- net/sctp/outqueue.c | 2 +- net/tipc/node.c | 2 +- 35 files changed, 74 insertions(+), 62 deletions(-) -- 2.53.0