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Subject[PATCH v2] trace: tracing_event_filter: fast path when no subsystem filters
Date
From: Nicholas Lowell <nlowell@lexmark.com>

If there are no filters in the event subsystem, then there's no
reason to continue and hit the potentially time consuming
tracepoint_synchronize_unregister function. This should give
a speed up for initial disabling/configuring

Signed-off-by: Nicholas Lowell <nlowell@lexmark.com>
---

Notes:
v2: switch from needless counting to boolean
WARN_ON_ONCE if no preds but filter exists

kernel/trace/trace_events_filter.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 33264e510d16..baa108f88032 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1317,22 +1317,29 @@ void free_event_filter(struct event_filter *filter)
__free_filter(filter);
}

-static inline void __remove_filter(struct trace_event_file *file)
+static inline bool __remove_filter(struct trace_event_file *file)
{
filter_disable(file);
+ if (!file->filter)
+ return false;
+
remove_filter_string(file->filter);
+ return true;
}

-static void filter_free_subsystem_preds(struct trace_subsystem_dir *dir,
+static bool filter_free_subsystem_preds(struct trace_subsystem_dir *dir,
struct trace_array *tr)
{
struct trace_event_file *file;
+ bool do_sync = false;

list_for_each_entry(file, &tr->events, list) {
if (file->system != dir)
continue;
- __remove_filter(file);
+ if (__remove_filter(file))
+ do_sync = true;
}
+ return do_sync;
}

static inline void __free_subsystem_filter(struct trace_event_file *file)
@@ -2411,7 +2418,12 @@ int apply_subsystem_event_filter(struct trace_subsystem_dir *dir,
}

if (!strcmp(strstrip(filter_string), "0")) {
- filter_free_subsystem_preds(dir, tr);
+ /* If nothing was freed, we do not need to sync */
+ if (!filter_free_subsystem_preds(dir, tr)) {
+ if(!(WARN_ON_ONCE(system->filter)))
+ goto out_unlock;
+ }
+
remove_filter_string(system->filter);
filter = system->filter;
system->filter = NULL;
--
2.25.1
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