[PATCH v2 00/19] tracepoint: Avoid double static_branch evaluation at guarded call sites

[PATCH v2 00/19] tracepoint: Avoid double static_branch evaluation at guarded call sites

[Vineeth Pillai (Google)]

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 <rostedt@goodmis.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>

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

[PATCH v2 01/19] tracepoint: Add trace_call__##name() API

[Vineeth Pillai (Google)]

Add trace_call__##name() as a companion to trace_##name().  When a
caller already guards a tracepoint with an explicit enabled check:

  if (trace_foo_enabled() && cond)
      trace_foo(args);

trace_foo() internally repeats the static_branch_unlikely() test, which
the compiler cannot fold since static branches are patched binary
instructions.  This results in two static-branch evaluations for every
guarded call site.

trace_call__##name() calls __do_trace_##name() directly, skipping the
redundant static-branch re-check.  This avoids leaking the internal
__do_trace_##name() symbol into call sites while still eliminating the
double evaluation:

  if (trace_foo_enabled() && cond)
      trace_invoke_foo(args);   /* calls __do_trace_foo() directly */

Three locations are updated:
- __DECLARE_TRACE: invoke form omits static_branch_unlikely, retains
  the LOCKDEP RCU-watching assertion.
- __DECLARE_TRACE_SYSCALL: same, plus retains might_fault().
- !TRACEPOINTS_ENABLED stub: empty no-op so callers compile cleanly
  when tracepoints are compiled out.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Vineeth Pillai (Google) <vineeth@bitbyteword.org>
Assisted-by: Claude:claude-sonnet-4-6
---
 include/linux/tracepoint.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 22ca1c8b54f32..ed969705341f1 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -294,6 +294,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 			WARN_ONCE(!rcu_is_watching(),			\
 				  "RCU not watching for tracepoint");	\
 		}							\
+	}								\
+	static inline void trace_call__##name(proto)			\
+	{								\
+		__do_trace_##name(args);				\
 	}
 
 #define __DECLARE_TRACE_SYSCALL(name, proto, args, data_proto)		\
@@ -313,6 +317,11 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 			WARN_ONCE(!rcu_is_watching(),			\
 				  "RCU not watching for tracepoint");	\
 		}							\
+	}								\
+	static inline void trace_call__##name(proto)			\
+	{								\
+		might_fault();						\
+		__do_trace_##name(args);				\
 	}
 
 /*
@@ -398,6 +407,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 #define __DECLARE_TRACE_COMMON(name, proto, args, data_proto)		\
 	static inline void trace_##name(proto)				\
 	{ }								\
+	static inline void trace_call__##name(proto)			\
+	{ }								\
 	static inline int						\
 	register_trace_##name(void (*probe)(data_proto),		\
 			      void *data)				\
-- 
2.53.0

Re: [PATCH v2 01/19] tracepoint: Add trace_call__##name() API

[Masami Hiramatsu]

On Mon, 23 Mar 2026 12:00:20 -0400
"Vineeth Pillai (Google)" <vineeth@bitbyteword.org> wrote:

> Add trace_call__##name() as a companion to trace_##name().  When a
> caller already guards a tracepoint with an explicit enabled check:
> 
>   if (trace_foo_enabled() && cond)
>       trace_foo(args);
> 
> trace_foo() internally repeats the static_branch_unlikely() test, which
> the compiler cannot fold since static branches are patched binary
> instructions.  This results in two static-branch evaluations for every
> guarded call site.
> 
> trace_call__##name() calls __do_trace_##name() directly, skipping the
> redundant static-branch re-check.  This avoids leaking the internal
> __do_trace_##name() symbol into call sites while still eliminating the
> double evaluation:
> 
>   if (trace_foo_enabled() && cond)
>       trace_invoke_foo(args);   /* calls __do_trace_foo() directly */

nit: trace_call_foo() instead of trace_invoke_foo()?

Anyway looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>


> 
> Three locations are updated:
> - __DECLARE_TRACE: invoke form omits static_branch_unlikely, retains
>   the LOCKDEP RCU-watching assertion.
> - __DECLARE_TRACE_SYSCALL: same, plus retains might_fault().
> - !TRACEPOINTS_ENABLED stub: empty no-op so callers compile cleanly
>   when tracepoints are compiled out.
> 
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Vineeth Pillai (Google) <vineeth@bitbyteword.org>
> Assisted-by: Claude:claude-sonnet-4-6
> ---
>  include/linux/tracepoint.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 22ca1c8b54f32..ed969705341f1 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -294,6 +294,10 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  			WARN_ONCE(!rcu_is_watching(),			\
>  				  "RCU not watching for tracepoint");	\
>  		}							\
> +	}								\
> +	static inline void trace_call__##name(proto)			\
> +	{								\
> +		__do_trace_##name(args);				\
>  	}
>  
>  #define __DECLARE_TRACE_SYSCALL(name, proto, args, data_proto)		\
> @@ -313,6 +317,11 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  			WARN_ONCE(!rcu_is_watching(),			\
>  				  "RCU not watching for tracepoint");	\
>  		}							\
> +	}								\
> +	static inline void trace_call__##name(proto)			\
> +	{								\
> +		might_fault();						\
> +		__do_trace_##name(args);				\
>  	}
>  
>  /*
> @@ -398,6 +407,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
>  #define __DECLARE_TRACE_COMMON(name, proto, args, data_proto)		\
>  	static inline void trace_##name(proto)				\
>  	{ }								\
> +	static inline void trace_call__##name(proto)			\
> +	{ }								\
>  	static inline int						\
>  	register_trace_##name(void (*probe)(data_proto),		\
>  			      void *data)				\
> -- 
> 2.53.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH v2 18/19] mm: damon: Use trace_call__##name() at guarded tracepoint call sites

[Vineeth Pillai (Google)]

Replace trace_damos_stat_after_apply_interval() with
trace_call__damos_stat_after_apply_interval() at a site already guarded
by an early return when !trace_damos_stat_after_apply_interval_enabled(),
avoiding a redundant static_branch_unlikely() re-evaluation inside the
tracepoint.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Vineeth Pillai (Google) <vineeth@bitbyteword.org>
---
 mm/damon/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index adfc52fee9dc2..b1cc4f44f90a2 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2342,7 +2342,7 @@ static void damos_trace_stat(struct damon_ctx *c, struct damos *s)
 			break;
 		sidx++;
 	}
-	trace_damos_stat_after_apply_interval(cidx, sidx, &s->stat);
+	trace_call__damos_stat_after_apply_interval(cidx, sidx, &s->stat);
 }
 
 static void kdamond_apply_schemes(struct damon_ctx *c)
-- 
2.53.0

Re: [PATCH v2 18/19] mm: damon: Use trace_call__##name() at guarded tracepoint call sites

[SeongJae Park]

On Mon, 23 Mar 2026 12:00:37 -0400 "Vineeth Pillai (Google)" <vineeth@bitbyteword.org> wrote:

> Replace trace_damos_stat_after_apply_interval() with
> trace_call__damos_stat_after_apply_interval() at a site already guarded
> by an early return when !trace_damos_stat_after_apply_interval_enabled(),
> avoiding a redundant static_branch_unlikely() re-evaluation inside the
> tracepoint.
> 
> Suggested-by: Steven Rostedt <rostedt@goodmis.org>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Vineeth Pillai (Google) <vineeth@bitbyteword.org>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]

Re: [PATCH v2 00/19] tracepoint: Avoid double static_branch evaluation at guarded call sites

[Steven Rostedt]

On Mon, 23 Mar 2026 12:00:19 -0400
"Vineeth Pillai (Google)" <vineeth@bitbyteword.org> wrote:

> When a caller already guards a tracepoint with an explicit enabled check:
> 
>   if (trace_foo_enabled() && cond)
>       trace_foo(args);

Thanks Vineeth!

I'm going to start pulling in this series. I'll take the first patch, and
then any patch that has an Acked-by or Reviewed-by from the maintainer.

For patches without acks, I'll leave alone and then after the first patch
gets merged into mainline, the maintainers could pull in their own patches
at their own convenience. Unless of course they speak up now if they want
me to take them ;-)

-- Steve

Re: [PATCH v2 00/19] tracepoint: Avoid double static_branch evaluation at guarded call sites

[Steven Rostedt]

On Mon, 23 Mar 2026 12:00:19 -0400
"Vineeth Pillai (Google)" <vineeth@bitbyteword.org> wrote:

>   if (trace_foo_enabled() && cond)
>       trace_call__foo(args);   /* calls __do_trace_foo() directly */

Hi Vineeth,

Could you rebase this series on top of 7.1-rc1 when it comes out?
Several of these patches were accepted already. Obviously drop those.
They were the patches that added the feature, and any where the
maintainer acked the patch.

Now that the feature has been accepted, if you post the patch series
again after 7.1-rc1 with all the patches that haven't been accepted
yet, then the maintainers can simply take them directly. As the feature
is now accepted, there's no dependency on it, and they don't need to go
through the tracing tree.

Thanks,

-- Steve