linux-kernel - Re: [PATCH v3 4/8] sched, x86: use arch_update_cpu_topology to indicate x86 need sched domain rebuild

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Date:   Mon, 12 Sep 2016 14:00:31 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     rjw@...ysocki.net, mingo@...hat.com, bp@...e.de, x86@...nel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, peterz@...radead.org
Subject: Re: [PATCH v3 4/8] sched, x86: use arch_update_cpu_topology to
 indicate x86 need sched domain rebuild

On Sat, 2016-09-10 at 18:20 +0200, Thomas Gleixner wrote:
> On Thu, 8 Sep 2016, Srinivas Pandruvada wrote:
> 
> How is this related to sched? And please stop writing lengthy sentences in
> the subject line.


> > From: Tim Chen <tim.c.chen@...ux.intel.com>
> > 
> > Provides x86 with arch_update_cpu_topology function. This function
> > allows us to indicate that a condition is detected that the sched
> > domain of x86 needs a complete rebuild.
> scheduler domains are not x86 specific .... 


> > 
> > This is done by setting the x86_topology_update flag.
> So without reading the patch I expect that the function sets the
> x86_topology_update flag. Crap.
> 
> What you really want to say is:
> 
>   The scheduler calls arch_update_cpu_topology() to check whether the
>   scheduler domains have to be rebuilt.
> 
>   So far x86 has no requirement for this, but the upcoming IMTI support
>   makes this necessary.
> 
>   Request the rebuild when the x86 internal update flag is set.
> 
> Or something along these lines. Changelog is a important part of a patch,
> really..

Sure.  Will do.

> 
> > 
> > +/* Flag to indicate if a complete sched domain rebuild is required */
> > +bool x86_topology_update;
> > +
> > +int arch_update_cpu_topology(void)
> > +{
> > +	if (x86_topology_update) {
> > +		x86_topology_update = false;
> > +		return 1;
> > +	} else
> > +		return 0;
> That lacks braces around the else path, but why aren't you just doing the
> obvious:
> 
> 	if (!x86_topology_update)
> 		return false;
> 	
> 	x86_topology_update = false;
> 	return true;
> 
> That would be too simple to read, right?;

Sure.  Will do.


> 
> Thanks,
> 
> 	tglx