diff options
| author | Steven Rostedt <rostedt@goodmis.org> | 2026-02-08 13:38:35 -0500 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2026-02-08 21:01:13 -0500 |
| commit | c4f1fe47b106e9200cbb1b8951bd75f036d53bd3 (patch) | |
| tree | 3c2a16a023aa4e83e9dff01b92bd0d3932903017 /kernel/trace/Kconfig | |
| parent | e4c1a09afbe2f02fc66b5ccbc96aa3a7109f9b79 (diff) | |
tracing: Better separate SNAPSHOT and MAX_TRACE options
The latency tracers (scheduler, irqsoff, etc) were created when tracing
was first added. These tracers required a "snapshot" buffer that was the
same size as the ring buffer being written to. When a new max latency was
hit, the main ring buffer would swap with the snapshot buffer so that the
trace leading up to the latency would be saved in the snapshot buffer (The
snapshot buffer is never written to directly and the data within it can be
viewed without fear of being overwritten).
Later, a new feature was added to allow snapshots to be taken by user
space or even event triggers. This created a "snapshot" file that allowed
users to trigger a snapshot from user space to save the current trace.
The config for this new feature (CONFIG_TRACER_SNAPSHOT) would select the
latency tracer config (CONFIG_TRACER_MAX_LATENCY) as it would need all the
functionality from it as it already existed. But this was incorrect. As
the snapshot feature is really what the latency tracers need and not the
other way around.
Have CONFIG_TRACER_MAX_TRACE select CONFIG_TRACER_SNAPSHOT where the
tracers that needs the max latency buffer selects the TRACE_MAX_TRACE
which will then select TRACER_SNAPSHOT.
Also, go through trace.c and trace.h and make the code that only needs the
TRACER_MAX_TRACE protected by that and the code that always requires the
snapshot to be protected by TRACER_SNAPSHOT.
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20260208183856.767870992@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/Kconfig')
| -rw-r--r-- | kernel/trace/Kconfig | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index bfa2ec46e075..bedb2f982823 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -133,6 +133,7 @@ config BUILDTIME_MCOUNT_SORT config TRACER_MAX_TRACE bool + select TRACER_SNAPSHOT config TRACE_CLOCK bool @@ -422,7 +423,6 @@ config IRQSOFF_TRACER select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP - select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP help This option measures the time spent in irqs-off critical @@ -445,7 +445,6 @@ config PREEMPT_TRACER select GENERIC_TRACER select TRACER_MAX_TRACE select RING_BUFFER_ALLOW_SWAP - select TRACER_SNAPSHOT select TRACER_SNAPSHOT_PER_CPU_SWAP select TRACE_PREEMPT_TOGGLE help @@ -467,7 +466,6 @@ config SCHED_TRACER select GENERIC_TRACER select CONTEXT_SWITCH_TRACER select TRACER_MAX_TRACE - select TRACER_SNAPSHOT help This tracer tracks the latency of the highest priority task to be scheduled in, starting from the point it has woken up. @@ -617,7 +615,6 @@ config TRACE_SYSCALL_BUF_SIZE_DEFAULT config TRACER_SNAPSHOT bool "Create a snapshot trace buffer" - select TRACER_MAX_TRACE help Allow tracing users to take snapshot of the current buffer using the ftrace interface, e.g.: @@ -625,6 +622,9 @@ config TRACER_SNAPSHOT echo 1 > /sys/kernel/tracing/snapshot cat snapshot + Note, the latency tracers select this option. To disable it, + all the latency tracers need to be disabled. + config TRACER_SNAPSHOT_PER_CPU_SWAP bool "Allow snapshot to swap per CPU" depends on TRACER_SNAPSHOT |