Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] ring_buffer: Use try_cmpxchg instead of cmpxchg in rb_insert_pages | Date | Thu, 14 Sep 2023 18:34:02 +0200 |
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Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in rb_insert_pages. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg).
No functional change intended.
Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- kernel/trace/ring_buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index a1651edc48d5..3e2a6478425c 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2048,7 +2048,7 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer) retries = 10; success = false; while (retries--) { - struct list_head *head_page, *prev_page, *r; + struct list_head *head_page, *prev_page; struct list_head *last_page, *first_page; struct list_head *head_page_with_bit; struct buffer_page *hpage = rb_set_head_page(cpu_buffer); @@ -2067,9 +2067,9 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer) last_page->next = head_page_with_bit; first_page->prev = prev_page; - r = cmpxchg(&prev_page->next, head_page_with_bit, first_page); - - if (r == head_page_with_bit) { + /* caution: head_page_with_bit gets updated on cmpxchg failure */ + if (try_cmpxchg(&prev_page->next, + &head_page_with_bit, first_page)) { /* * yay, we replaced the page pointer to our new list, * now, we just have to update to head page's prev -- 2.41.0
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