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ring_buffer: Use try_cmpxchg instead of cmpxchg in rb_insert_pages

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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.

Link: https://lore.kernel.org/linux-trace-kernel/20230914163420.12923-1-ubizjak@gmail.com

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Uros Bizjak 2023-09-14 18:34:02 +02:00 committed by Steven Rostedt (Google)
parent a1f157c7a3
commit bdf4fb6280
1 changed files with 4 additions and 4 deletions
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8
kernel/trace/ring_buffer.c
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@ -2056,7 +2056,7 @@ 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);
@ -2075,9 +2075,9 @@ 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