The commit c1de45ca831a ("sched/idle: Add support for
tasks that inject idle") redesigns the code for idle
loop to support for tasks that inject idle.
it fetches the current CPU using smp_processor_id( )
every time when the idle task runs.
Now idle task is no longer limited to PID == 0,
but the current CPU is constant, so fetch the
smp_prcessor_id( ) out of the loop like the
commit df55f462b905 ("sched/idle: Optimize the
generic idle loop") do.
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.chengj...@huawei.com>
---
kernel/sched/idle.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 257f4f0..41f16b8 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -209,6 +209,7 @@ static void cpuidle_idle_call(void)
*/
static void do_idle(void)
{
+ int cpu = smp_processor_id();
/*
* If the arch has a polling bit, we maintain an invariant:
*
@@ -226,7 +227,7 @@ 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();
}
--
1.8.3.1
