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From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Nicolas Saenz Julienne <nsaenzju@redhat.com>
Subject: [for-linus][PATCH 5/7] ftrace: Avoid synchronize_rcu_tasks_rude() call when not necessary
Date: Fri, 23 Jul 2021 08:54:59 -0400	[thread overview]
Message-ID: <20210723125634.213430293@goodmis.org> (raw)
In-Reply-To: <20210723125454.570472450@goodmis.org>

From: Nicolas Saenz Julienne <nsaenzju@redhat.com>

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.

Link: https://lkml.kernel.org/r/20210721114726.1545103-1-nsaenzju@redhat.com

Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 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);
 	}
-- 
2.30.2

  parent reply	other threads:[~2021-07-23 12:56 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-23 12:54 [for-linus][PATCH 0/7] tracing: Fixes for 5.14-rc2 Steven Rostedt
2021-07-23 12:54 ` [for-linus][PATCH 1/7] tracing: Fix bug in rb_per_cpu_empty() that might cause deadloop Steven Rostedt
2021-07-23 12:54 ` [for-linus][PATCH 2/7] tracing: Synthetic event field_pos is an index not a boolean Steven Rostedt
2021-07-23 12:54 ` [for-linus][PATCH 3/7] tracing/histogram: Rename "cpu" to "common_cpu" Steven Rostedt
2021-07-23 12:54 ` [for-linus][PATCH 4/7] tracing: Clean up alloc_synth_event() Steven Rostedt
2021-07-23 12:54 ` Steven Rostedt [this message]
2021-07-23 12:55 ` [for-linus][PATCH 6/7] ftrace: Remove redundant initialization of variable ret Steven Rostedt
2021-07-23 12:55 ` [for-linus][PATCH 7/7] tracepoints: Update static_call before tp_funcs when adding a tracepoint Steven Rostedt

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