* [PATCH] ftrace: Avoid synchronize_rcu_tasks_rude() call when not necessary
@ 2021-07-21 11:47 Nicolas Saenz Julienne
0 siblings, 0 replies; only message in thread
From: Nicolas Saenz Julienne @ 2021-07-21 11:47 UTC (permalink / raw)
To: rostedt, mingo; +Cc: linux-kernel, Nicolas Saenz Julienne
synchronize_rcu_tasks_rude() triggers IPIs and forces rescheduling on
all CPUs. It is a costly operation and, when targeting nohz_full CPUs,
very disrupting (hence the name). So avoid calling it when 'old_hash'
doesn't need to be freed.
Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
---
kernel/trace/ftrace.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index e6fb3e6e1ffc..4fbcf560dd03 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5985,7 +5985,8 @@ ftrace_graph_release(struct inode *inode, struct file *file)
* infrastructure to do the synchronization, thus we must do it
* ourselves.
*/
- synchronize_rcu_tasks_rude();
+ if (old_hash != EMPTY_HASH)
+ synchronize_rcu_tasks_rude();
free_ftrace_hash(old_hash);
}
--
2.31.1
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