diff options
| author | Cheng Jian <cj.chengjian@huawei.com> | 2017-10-25 19:28:27 +0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-10-26 08:31:29 +0200 |
| commit | 54b933c6c954a8b7b0c2b40a1c4d3f7279d11e22 (patch) | |
| tree | 74daae35b6a9df8ef3647ef12e1d010187fb5481 /kernel/sched | |
| parent | e22cdc3fc5991956146b9856d36b4971fe54dcd6 (diff) | |
sched/idle: Micro-optimize the idle loop
Move the loop-invariant calculation of 'cpu' in do_idle() out of the loop body,
because the current CPU is always constant.
This improves the generated code both on x86-64 and ARM64:
x86-64:
Before patch (execution in loop):
864: 0f ae e8 lfence
867: 65 8b 05 c2 38 f1 7e mov %gs:0x7ef138c2(%rip),%eax
86e: 89 c0 mov %eax,%eax
870: 48 0f a3 05 68 19 08 bt %rax,0x1081968(%rip)
877: 01
After patch (execution in loop):
872: 0f ae e8 lfence
875: 4c 0f a3 25 63 19 08 bt %r12,0x1081963(%rip)
87c: 01
ARM64:
Before patch (execution in loop):
c58: d5033d9f dsb ld
c5c: d538d080 mrs x0, tpidr_el1
c60: b8606a61 ldr w1, [x19,x0]
c64: 1100fc20 add w0, w1, #0x3f
c68: 7100003f cmp w1, #0x0
c6c: 1a81b000 csel w0, w0, w1, lt
c70: 13067c00 asr w0, w0, #6
c74: 93407c00 sxtw x0, w0
c78: f8607a80 ldr x0, [x20,x0,lsl #3]
c7c: 9ac12401 lsr x1, x0, x1
c80: 36000581 tbz w1, #0, d30 <do_idle+0x128>
After patch (execution in loop):
c84: d5033d9f dsb ld
c88: f9400260 ldr x0, [x19]
c8c: ea14001f tst x0, x20
c90: 54000580 b.eq d40 <do_idle+0x138>
Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
[ Rewrote the title and the changelog. ]
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: huawei.libin@huawei.com
Cc: xiexiuqi@huawei.com
Link: http://lkml.kernel.org/r/1508930907-107755-1-git-send-email-cj.chengjian@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/idle.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index b2e8f0afbb42..7dae9eb8c042 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -209,6 +209,7 @@ exit_idle: */ static void do_idle(void) { + int cpu = smp_processor_id(); /* * If the arch has a polling bit, we maintain an invariant: * @@ -225,7 +226,7 @@ static void do_idle(void) check_pgt_cache(); rmb(); - if (cpu_is_offline(smp_processor_id())) { + if (cpu_is_offline(cpu)) { cpuhp_report_idle_dead(); arch_cpu_idle_dead(); } |