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Date:   Thu, 26 Nov 2020 09:57:31 +1100
From:   Balbir Singh <bsingharora@gmail.com>
To:     "Li, Aubrey" <aubrey.li@linux.intel.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Vineeth Pillai <viremana@linux.microsoft.com>,
        Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.intel@gmail.com>, tglx@linutronix.de,
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        Valentin Schneider <valentin.schneider@arm.com>,
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        Aubrey Li <aubrey.li@intel.com>,
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        Tim Chen <tim.c.chen@intel.com>
Subject: Re: [PATCH -tip 14/32] sched: migration changes for core scheduling
Message-ID: <20201125225731.GB163610@balbir-desktop>
References: <20201117232003.3580179-1-joel@joelfernandes.org>
 <20201117232003.3580179-15-joel@joelfernandes.org>
 <20201122235456.GF110669@balbir-desktop>
 <0b2514ef-6cc3-c1a3-280b-5d9062c80a31@linux.intel.com>
 <20201124154237.GZ3021@hirez.programming.kicks-ass.net>
 <d541b70c-c65f-5bf6-5e71-0b9b35457fae@linux.intel.com>
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On Wed, Nov 25, 2020 at 11:12:53AM +0800, Li, Aubrey wrote:
> On 2020/11/24 23:42, Peter Zijlstra wrote:
> > On Mon, Nov 23, 2020 at 12:36:10PM +0800, Li, Aubrey wrote:
> >>>> +#ifdef CONFIG_SCHED_CORE
> >>>> +		/*
> >>>> +		 * Skip this cpu if source task's cookie does not match
> >>>> +		 * with CPU's core cookie.
> >>>> +		 */
> >>>> +		if (!sched_core_cookie_match(cpu_rq(cpu), env->p))
> >>>> +			continue;
> >>>> +#endif
> >>>> +
> >>>
> >>> Any reason this is under an #ifdef? In sched_core_cookie_match() won't
> >>> the check for sched_core_enabled() do the right thing even when
> >>> CONFIG_SCHED_CORE is not enabed?> 
> >> Yes, sched_core_enabled works properly when CONFIG_SCHED_CORE is not
> >> enabled. But when CONFIG_SCHED_CORE is not enabled, it does not make
> >> sense to leave a core scheduler specific function here even at compile
> >> time. Also, for the cases in hot path, this saves CPU cycles to avoid
> >> a judgment.
> > 
> > No, that's nonsense. If it works, remove the #ifdef. Less (#ifdef) is
> > more.
> > 
> 
> Okay, I pasted the refined patch here.
> @Joel, please let me know if you want me to send it in a separated thread.
>

You still have a bunch of #ifdefs, can't we just do

#ifndef CONFIG_SCHED_CORE
static inline bool sched_core_enabled(struct rq *rq)
{
        return false;
}
#endif

and frankly I think even that is not needed because there is a jump
label __sched_core_enabled that tells us if sched_core is enabled or
not.

Balbir