linux-kernel - Re: [PATCH 1/3] sched/rt: cpupri_find: implement fallback mechanism for !fit case

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Date:   Tue, 18 Feb 2020 18:52:54 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched/rt: cpupri_find: implement fallback mechanism
 for !fit case

On 02/18/20 13:03, Steven Rostedt wrote:
> On Tue, 18 Feb 2020 17:27:46 +0000
> Qais Yousef <qais.yousef@....com> wrote:
> 
> > > If we are going to use static branches, then lets just remove the
> > > parameter totally. That is, make two functions (with helpers), where
> > > one needs this fitness function the other does not.
> > > 
> > > 	if (static_branch_unlikely(&sched_asym_cpu_capacity))
> > > 		ret = cpupri_find_fitness(...);
> > > 	else
> > > 		ret = cpupri_find(...);
> > > 
> > > 	if (!ret)
> > > 		return -1;
> > > 
> > > Something like that?  
> > 
> > Is there any implication on code generation here?
> > 
> > I like my flavour better tbh. But I don't mind refactoring the function out if
> > it does make it more readable.
> 
> I just figured we remove the passing of the parameter (which does make
> an impact on the code generation).

Ok. My mind went to protecting the whole function call with the static key
could be better.

> Also, perhaps it would be better to not have to pass functions to the
> cpupri_find(). Is there any other function that needs to be past, or
> just this one in this series?

I had that discussion in the past with Dietmar [1]

My argument was this way the code is generic and self contained and allows for
easy extension for other potential users.

I'm happy to split the function into cpupri_find_fitness() (with a fn ptr) and
cpupri_find() (original) like you suggest above - if you're still okay with
that..

[1] https://lore.kernel.org/lkml/39c08971-5d07-8018-915b-9c6284f89d5d@arm.com/

Thanks

--
Qais Youesf