summaryrefslogtreecommitdiffstats
path: root/kernel/sched/idle.c
diff options
context:
space:
mode:
authorCheng Jian <cj.chengjian@huawei.com>2017-10-25 19:28:27 +0800
committerIngo Molnar <mingo@kernel.org>2017-10-26 08:31:29 +0200
commit54b933c6c954a8b7b0c2b40a1c4d3f7279d11e22 (patch)
tree74daae35b6a9df8ef3647ef12e1d010187fb5481 /kernel/sched/idle.c
parente22cdc3fc5991956146b9856d36b4971fe54dcd6 (diff)
downloadlinux-54b933c6c954a8b7b0c2b40a1c4d3f7279d11e22.tar.bz2
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/idle.c')
-rw-r--r--kernel/sched/idle.c3
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();
}