Re: [PATCH v10 10/11] arm64: idle: export arch_cpu_idle()

[Shuai Xue <xueshuai@linux.alibaba.com>]

在 2025/4/12 04:57, Ankur Arora 写道:
> 
> Shuai Xue <xueshuai@linux.alibaba.com> writes:
> 
>> 在 2025/2/19 05:33, Ankur Arora 写道:
>>> Needed for cpuidle-haltpoll.
>>> Acked-by: Will Deacon <will@kernel.org>
>>> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
>>> ---
>>>    arch/arm64/kernel/idle.c | 1 +
>>>    1 file changed, 1 insertion(+)
>>> diff --git a/arch/arm64/kernel/idle.c b/arch/arm64/kernel/idle.c
>>> index 05cfb347ec26..b85ba0df9b02 100644
>>> --- a/arch/arm64/kernel/idle.c
>>> +++ b/arch/arm64/kernel/idle.c
>>> @@ -43,3 +43,4 @@ void __cpuidle arch_cpu_idle(void)
>>>    	 */
>>>    	cpu_do_idle();
>>
>> Hi, Ankur,
>>
>> With haltpoll_driver registered, arch_cpu_idle() on x86 can select
>> mwait_idle() in idle threads.
>>
>> It use MONITOR sets up an effective address range that is monitored
>> for write-to-memory activities; MWAIT places the processor in
>> an optimized state (this may vary between different implementations)
>> until a write to the monitored address range occurs.
> 
> MWAIT is more capable than WFE -- it allows selection of deeper idle
> state. IIRC C2/C3.
> 
>> Should arch_cpu_idle() on arm64 also use the LDXR/WFE
>> to avoid wakeup IPI like x86 monitor/mwait?
> 
> Avoiding the wakeup IPI needs TIF_NR_POLLING and polling in idle support
> that this series adds.
> 
> As Haris notes, the negative with only using WFE is that it only allows
> a single idle state, one that is fairly shallow because the event-stream
> causes a wakeup every 100us.
> 
> --
> ankur

Hi, Ankur and Haris

Got it, thanks for explaination :)

Comparing sched-pipe performance on Rund with Yitian 710, *IPC improved 35%*:

w/o haltpoll
Performance counter stats for 'CPU(s) 0,1' (5 runs):

     32521.53 msec task-clock                #    2.000 CPUs utilized            ( +-  1.16% )
  38081402726      cycles                    #    1.171 GHz                      ( +-  1.70% )
  27324614561      instructions              #    0.72  insn per cycle           ( +-  0.12% )
          181      sched:sched_wake_idle_without_ipi #    0.006 K/sec

w/ haltpoll
Performance counter stats for 'CPU(s) 0,1' (5 runs):

      9477.15 msec task-clock                #    2.000 CPUs utilized            ( +-  0.89% )
  21486828269      cycles                    #    2.267 GHz                      ( +-  0.35% )
  23867109747      instructions              #    1.11  insn per cycle           ( +-  0.11% )
      1925207      sched:sched_wake_idle_without_ipi #    0.203 M/sec

Comparing sched-pipe performance on QEMU with Kunpeng 920, *IPC improved 10%*:

w/o haltpoll
Performance counter stats for 'CPU(s) 0,1' (5 runs):

          34,007.89 msec task-clock                       #    2.000 CPUs utilized               ( +-  8.86% )
      4,407,859,620      cycles                           #    0.130 GHz                         ( +- 84.92% )
      2,482,046,461      instructions                     #    0.56  insn per cycle              ( +- 88.27% )
                 16      sched:sched_wake_idle_without_ipi #    0.470 /sec                        ( +- 98.77% )

              17.00 +- 1.51 seconds time elapsed  ( +-  8.86% )

w/ haltpoll
Performance counter stats for 'CPU(s) 0,1' (5 runs):

          16,894.37 msec task-clock                       #    2.000 CPUs utilized               ( +-  3.80% )
      8,703,158,826      cycles                           #    0.515 GHz                         ( +- 31.31% )
      5,379,257,839      instructions                     #    0.62  insn per cycle              ( +- 30.03% )
            549,434      sched:sched_wake_idle_without_ipi #   32.522 K/sec                       ( +- 30.05% )

              8.447 +- 0.321 seconds time elapsed  ( +-  3.80% )

Tested-by: Shuai Xue <xueshuai@linux.alibaba.com>

Thanks.
Shuai