linux-kernel - Re: [PATCH v10 10/11] arm64: idle: export arch_cpu

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Message-ID: <87639d1b017b6032c1d5382567415fad4e2c9e4e.camel@amazon.com>
Date: Fri, 11 Apr 2025 17:42:17 +0000
From: "Okanovic, Haris" <harisokn@...zon.com>
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Subject: Re: [PATCH v10 10/11] arm64: idle: export arch_cpu_idle()

On Fri, 2025-04-11 at 11:32 +0800, Shuai Xue wrote:
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> > 
> > 
> > 
> > 在 2025/2/19 05:33, Ankur Arora 写道:
> > > > Needed for cpuidle-haltpoll.
> > > > 
> > > > Acked-by: Will Deacon <will@...nel.org>
> > > > Signed-off-by: Ankur Arora <ankur.a.arora@...cle.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.
> > 
> > Should arch_cpu_idle() on arm64 also use the LDXR/WFE
> > to avoid wakeup IPI like x86 monitor/mwait?

WFE will wake from the event stream, which can have short sub-ms
periods on many systems. May be something to consider when WFET is more
widely available.

> > 
> > Thanks.
> > Shuai
> > 
> > 

Regards,
Haris Okanovic
AWS Graviton Software