linux-kernel - Re: [PATCH 4/4] base/drivers/topology: Default dmpis-mhz if they are not set in DT

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Date:   Thu, 22 Nov 2018 09:59:00 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rjw@...ysocki.net, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org,
        Chris Redpath <chris.redpath@...aro.org>,
        Quentin Perret <quentin.perret@...aro.org>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Nicolas Dechesne <nicolas.dechesne@...aro.org>,
        Niklas Cassel <niklas.cassel@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 4/4] base/drivers/topology: Default dmpis-mhz if they are
 not set in DT

On 21-11-18, 23:12, Daniel Lezcano wrote:
> On 30/10/2018 09:58, Viresh Kumar wrote:
> > s/dmpis/dmips/ in $subject
> > 
> > On 29-10-18, 17:23, Daniel Lezcano wrote:
> >> In the case of assymetric SoC with the same micro-architecture, we
> > 
> >                  asymmetric ?
> > 
> >> have a group of CPUs with smaller OPPs than the other group. One
> >> example is the 96boards dragonboard 820c. There is no dmips/MHz
> >> difference between both groups, so no need to specify the values in
> >> the DT. Unfortunately, without these defined, there is no scaling
> >> capacity comutation triggered, so we need to write
> > 
> >            computation
> > 
> >> 'capacity-dmips-mhz' for each CPU with the same value in order to
> >> force the scaled capacity computation.
> >>
> >> Fix this by setting a default capacity to SCHED_CAPACITY_SCALE, if no
> >> 'capacity-dmips-mhz' is defined in the DT.
> >>
> >> This was tested on db820c:
> >>  - specified values in the DT (correct results)
> >>  - partial values defined in the DT (error + fallback to defaults)
> >>  - no specified values in the DT (correct results)
> >>
> >> correct results are:
> >>   cat /sys/devices/system/cpu/cpu*/cpu_capacity
> >>    758
> >>    758
> >>   1024
> >>   1024
> >>
> >>   ... respectively for CPU0, CPU1, CPU2 and CPU3.
> >>
> >> That reflects the capacity for the max frequencies 1593600 and 2150400.
> >>
> >> Cc: Chris Redpath <chris.redpath@...aro.org>
> >> Cc: Quentin Perret <quentin.perret@...aro.org>
> >> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> >> Cc: Amit Kucheria <amit.kucheria@...aro.org>
> >> Cc: Nicolas Dechesne <nicolas.dechesne@...aro.org>
> >> Cc: Niklas Cassel <niklas.cassel@...aro.org>
> >> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> >> ---
> >>  drivers/base/arch_topology.c | 27 ++++++++++++++++++++++++++-
> >>  1 file changed, 26 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> >> index 7311641..7d594a6 100644
> >> --- a/drivers/base/arch_topology.c
> >> +++ b/drivers/base/arch_topology.c
> >> @@ -205,6 +205,21 @@ static struct notifier_block init_cpu_capacity_notifier = {
> >>  	.notifier_call = init_cpu_capacity_callback,
> >>  };
> >>  
> >> +static int topology_set_default_capacity(void)
> >> +{
> >> +	int cpu;
> >> +
> >> +	raw_capacity = kzalloc(num_possible_cpus() * sizeof(*raw_capacity),
> >> +			       GFP_KERNEL);
> >> +	if (!raw_capacity)
> >> +		return -ENOMEM;
> >> +
> >> +	for_each_possible_cpu(cpu)
> >> +		raw_capacity[cpu] = SCHED_CAPACITY_SCALE;
> > 
> > This isn't actually required as the value of raw_capacity isn't used
> > anymore after this point in code. Rather it is forcefully updated in
> > init_cpu_capacity_callback():
> > 
> > raw_capacity[cpu] = topology_get_cpu_scale(NULL, cpu) *
> >                     policy->cpuinfo.max_freq / 1000UL;
> > 
> > Maybe it is better to allocate raw_capacity once at boot and use
> > another global variable as flag (raw_capacity is used as a flag right
> > now at many places).
> 
> Can we keep the proposed change as is to simply fix the default value?
> 
> I want to do a separate change with a raw_capacity rewrite and remove
> the workqueue freeing it.

Sure. But you still don't need to update raw_capacity[cpu] above as I pointed
out earlier. You can drop those lines at least.

-- 
viresh