diff options
| author | Masami Hiramatsu (Google) <mhiramat@kernel.org> | 2024-12-27 13:07:57 +0900 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-04-10 14:39:35 +0200 |
| commit | fe87f8d3a5b485eb8fc605d37437c8a70bf89731 (patch) | |
| tree | b1dd857dcf4f9ed24eb3c9fd53fb34fa7fea5a5c /include/linux/trace_events.h | |
| parent | 387dc88c2c27c33f6c0422fb79c6470b06b3c046 (diff) | |
tracing/hist: Add poll(POLLIN) support on hist file
[ Upstream commit 1bd13edbbed6e7e396f1aab92b224a4775218e68 ]
Add poll syscall support on the `hist` file. The Waiter will be waken
up when the histogram is updated with POLLIN.
Currently, there is no way to wait for a specific event in userspace.
So user needs to peek the `trace` periodicaly, or wait on `trace_pipe`.
But it is not a good idea to peek at the `trace` for an event that
randomly happens. And `trace_pipe` is not coming back until a page is
filled with events.
This allows a user to wait for a specific event on the `hist` file. User
can set a histogram trigger on the event which they want to monitor
and poll() on its `hist` file. Since this poll() returns POLLIN, the next
poll() will return soon unless a read() happens on that hist file.
NOTE: To read the hist file again, you must set the file offset to 0,
but just for monitoring the event, you may not need to read the
histogram.
Cc: Shuah Khan <shuah@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/173527247756.464571.14236296701625509931.stgit@devnote2
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Stable-dep-of: 0b4ffbe4888a ("tracing: Correct the refcount if the hist/hist_debug file fails to open")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'include/linux/trace_events.h')
| -rw-r--r-- | include/linux/trace_events.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 77769ff50544..fcf5a64d5cfe 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -689,6 +689,20 @@ struct trace_event_file { atomic_t tm_ref; /* trigger-mode reference counter */ }; +#ifdef CONFIG_HIST_TRIGGERS +extern struct irq_work hist_poll_work; +extern wait_queue_head_t hist_poll_wq; + +static inline void hist_poll_wakeup(void) +{ + if (wq_has_sleeper(&hist_poll_wq)) + irq_work_queue(&hist_poll_work); +} + +#define hist_poll_wait(file, wait) \ + poll_wait(file, &hist_poll_wq, wait) +#endif + #define __TRACE_EVENT_FLAGS(name, value) \ static int __init trace_init_flags_##name(void) \ { \ |