RE: [PATCH 1/2][v2] cpuidle-haltpoll: Replace default_idle with arch_cpu_idle

["Li,Rongqing" <lirongqing@baidu.com>]

> -----Original Message-----
> From: Rafael J. Wysocki <rafael@kernel.org>
> Sent: Wednesday, December 7, 2022 10:38 PM
> To: Li,Rongqing <lirongqing@baidu.com>
> Cc: tglx@linutronix.de; mingo@redhat.com; bp@alien8.de;
> dave.hansen@linux.intel.com; x86@kernel.org; rafael@kernel.org;
> daniel.lezcano@linaro.org; peterz@infradead.org; akpm@linux-foundation.org;
> tony.luck@intel.com; jpoimboe@kernel.org; linux-kernel@vger.kernel.org;
> linux-pm@vger.kernel.org
> Subject: Re: [PATCH 1/2][v2] cpuidle-haltpoll: Replace default_idle with
> arch_cpu_idle
> 
> On Wed, Dec 7, 2022 at 1:42 PM <lirongqing@baidu.com> wrote:
> >
> > From: Li RongQing <lirongqing@baidu.com>
> >
> > When KVM guest has MWAIT and mwait_idle is used as default idle
> > function, but once cpuidle-haltpoll is loaded, default_idle in
> > default_enter_idle is used, which is using HLT, and cause a
> > performance regression. As the commit aebef63cf7ff ("x86: Remove
> > vendor checks from prefer_mwait_c1_over_halt") explains that mwait is
> > preferred
> >
> > so replace default_idle with arch_cpu_idle which can using MWAIT
> > optimization.
> >
> > latency of sockperf ping-pong localhost test is reduced by more 20%
> > unixbench has 5% performance improvements for single core
> >
> > Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> > Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > ---
> >  arch/x86/kernel/process.c          | 1 +
> >  drivers/cpuidle/cpuidle-haltpoll.c | 2 +-
> >  2 files changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> > index c21b734..303afad 100644
> > --- a/arch/x86/kernel/process.c
> > +++ b/arch/x86/kernel/process.c
> > @@ -721,6 +721,7 @@ void arch_cpu_idle(void)  {
> >         x86_idle();
> >  }
> > +EXPORT_SYMBOL(arch_cpu_idle);
> 
> Why do you need this export at all?
> 

When cpuidle-haltpoll is built as module, if arch_cpu_idle is not export, cpuidle-haltpoll will complain "arch_cpu_idle" undefined

Like

ERROR: modpost: "arch_cpu_idle" [drivers/cpuidle/cpuidle-haltpoll.ko] undefined!
make[1]: *** [scripts/Makefile.modpost:126: Module.symvers] Error 1
make: *** [Makefile:1944: modpost] Error 2
Error: Make failed!

I will add the reason to v3 
Thanks

-Li