linux-kernel - Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

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Date:   Fri, 1 Sep 2017 13:57:48 +0800
From:   Quan Xu <quan.xu0@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Yang Zhang <yang.zhang.wz@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        wanpeng.li@...mail.com, mst@...hat.com, pbonzini@...hat.com,
        tglx@...utronix.de, rkrcmar@...hat.com, dmatlack@...gle.com,
        agraf@...e.de, linux-doc@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>, Kyle Huey <me@...ehuey.com>,
        Andy Lutomirski <luto@...nel.org>,
        Len Brown <len.brown@...el.com>
Subject: Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle
 path

on 2017/8/29 20:45, Peter Zijlstra wrote:

> On Tue, Aug 29, 2017 at 11:46:37AM +0000, Yang Zhang wrote:
>> Add poll in do_idle. For UP VM, if there are running task, it will not
>> goes into idle path, so we only enable poll in SMP VM.
>>
>> Signed-off-by: Yang Zhang <yang.zhang.wz@...il.com>
>> Signed-off-by: Quan Xu <quan.xu0@...il.com>
> Broken SoB chain.
   Peter,  I can't follow 'Broken SoB chain'.. could you more about it?

   -Quan

>> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
>> index 6c23e30..b374744 100644
>> --- a/kernel/sched/idle.c
>> +++ b/kernel/sched/idle.c
>> @@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
>>   }
>>   
>>   /* Weak implementations for optional arch specific functions */
>> +void __weak arch_cpu_idle_poll(void) { }
>>   void __weak arch_cpu_idle_prepare(void) { }
>>   void __weak arch_cpu_idle_enter(void) { }
> And not a word on why we need a new arch hook. What's wrong with
> arch_cpu_idle_enter() for instance?