diff options
| author | Zhongqiu Han <quic_zhonhan@quicinc.com> | 2024-10-09 17:37:45 +0800 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2024-10-14 12:52:40 +0200 |
| commit | 8e113df990c9df70fc6d83ebd53ee1b2867c23c4 (patch) | |
| tree | face08a8df64eb116b43e577ef60dae0acb661fa /kernel/sched/idle.c | |
| parent | 3144c83dcc9385c0b3291d36f3231411f5efdb40 (diff) | |
sched: idle: Optimize the generic idle loop by removing needless memory barrier
The memory barrier rmb() in generic idle loop do_idle() function is not
needed, it doesn't order any load instruction, just remove it as needless
rmb() can cause performance impact.
The rmb() was introduced by the tglx/history.git commit f2f1b44c75c4
("[PATCH] Remove RCU abuse in cpu_idle()") to order the loads between
cpu_idle_map and pm_idle. It pairs with wmb() in function cpu_idle_wait().
And then with the removal of cpu_idle_state in function cpu_idle() and
wmb() in function cpu_idle_wait() in commit 783e391b7b5b ("x86: Simplify
cpu_idle_wait"), rmb() no longer has a reason to exist.
After that, commit d16699123434 ("idle: Implement generic idle function")
implemented a generic idle function cpu_idle_loop() which resembles the
functionality found in arch/. And it retained the rmb() in generic idle
loop in file kernel/cpu/idle.c.
And at last, commit cf37b6b48428 ("sched/idle: Move cpu/idle.c to
sched/idle.c") moved cpu/idle.c to sched/idle.c. And commit c1de45ca831a
("sched/idle: Add support for tasks that inject idle") renamed function
cpu_idle_loop() to do_idle().
History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Signed-off-by: Zhongqiu Han <quic_zhonhan@quicinc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20241009093745.9504-1-quic_zhonhan@quicinc.com
Diffstat (limited to 'kernel/sched/idle.c')
| -rw-r--r-- | kernel/sched/idle.c | 1 |
1 files changed, 0 insertions, 1 deletions
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index d2f096bb274c..ab911d1335ba 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -271,7 +271,6 @@ static void do_idle(void) tick_nohz_idle_enter(); while (!need_resched()) { - rmb(); /* * Interrupts shouldn't be re-enabled from that point on until |