linux-kernel - Re: [PATCH v3 05/10] sched/fair: Hoist idle_stamp up from idle

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Message-ID: <c177b7dc-b75a-8f0a-e266-b70f2bac780b@arm.com>
Date:   Tue, 20 Nov 2018 10:24:50 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Steven Sistare <steven.sistare@...cle.com>, mingo@...hat.com,
        peterz@...radead.org
Cc:     subhra.mazumdar@...cle.com, dhaval.giani@...cle.com,
        daniel.m.jordan@...cle.com, pavel.tatashin@...rosoft.com,
        matt@...eblueprint.co.uk, umgwanakikbuti@...il.com,
        riel@...hat.com, jbacik@...com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, quentin.perret@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 05/10] sched/fair: Hoist idle_stamp up from
 idle_balance

On 19/11/2018 17:31, Steven Sistare wrote:
[...]
>>> +#define IF_SMP(statement)	statement
>>> +
>>
>> I'm not too hot on those IF_SMP() macros. Since you're not introducing
>> any other user for them, what about an inline function for rq->idle_stamp
>> setting ? When it's mapped to an empty statement (!CONFIG_SMP) GCC is
>> smart enough to remove the rq_clock() that would be passed to it on
>> CONFIG_SMP:
> 
> That may be true now, but I worry that rq_clock or its subroutines may gain
> side effects in the future that prevent the compiler from removing it.  However,
> I could push rq_clock into the inline function:
> 
>   static inline void rq_idle_stamp_set(rq)    { rq->idle_stamp = rq_clock(rq); }
>   static inline void rq_idle_stamp_clear(rq)  { rq->idle_stamp = 0; }
> 
> I like that better, do you?
> 

That works for me, though I can't resist nitpicking on
s/rq_idle_stamp_set/rq_idle_stamp_update/

> - Steve