Le 13 mai 2015 9:02 PM, "Jorge Ramirez-Ortiz" <jorge.ramirez-ortiz@linaro.org> a écrit :
>
> On 05/13/2015 12:39 PM, Jon Medhurst (Tixy) wrote:
> > On Wed, 2015-05-13 at 11:06 -0400, Jorge Ramirez-Ortiz wrote:
> >> From: Jorge Ramirez-Ortiz <jro@xenomai.org>
> >>
> >> The current arm64 power scaling calculations deviate from the arm
> >> implementation causing scheduling problems on non bigLITTLE
> >> architectures (this could be due to baseline/merging issues).
> > I've never really looked at this code before but I did some comparisons
> > of arm versus arm64 versions and LSK versus mainline and my observations
> > are:
> >
> > 1. There is no arm64 implementation in mainline. (Is there a reason?)
> >
> > 2. The arm64 implementation in LSK closely resembles the arm mainline
> > version, except that mainline doesn't have the
> >
> >       if (min_capacity == max_capacity)
> >               return;
> >       else
> >
> > That looks like an accidental side effect of commit
> > 816a8de0017f ("ARM: topology: remove hwid/MPIDR dependency from
> > cpu_capacity"). But it does meant that in mainline 'middle_capacity' is
> > now set by parse_dt_cpu_power (to a useful value?) rather than being
> > left as '1'.
> >
> > 3. The arm version in LSK looks like the ARM64 version, in the sense
> > that 'middle_capacity' is not set, so is this something which needs
> > addressing on arm as well?
>
> I'd think so.

AFAICT ARM 32bits in lsk still uses the old algorithm with hwid which prevent the situation seen on arm64

Vincent

> the patch below (scaling in the case where min_capacity == max_capacity) is one
> way of fixing it.
>
>
> >
> >> The proposed workaround uses the middle_capacity weighting factor to
> >> guarantee that all CPUs report the same power (1024)  on non bigLITTLE SoC.
> >>
> >> Signed-off-by: Jorge Ramirez-Ortiz <jro@xenomai.org>
> >> ---
> >>  arch/arm64/kernel/topology.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> >> index db8bb29..65837c2 100644
> >> --- a/arch/arm64/kernel/topology.c
> >> +++ b/arch/arm64/kernel/topology.c
> >> @@ -325,7 +325,7 @@ static void __init parse_dt_cpu_power(void)
> >>       * constraint explained near table_efficiency[].
> >>       */
> >>      if (min_capacity == max_capacity)
> >> -            return;
> >> +            middle_capacity = max_capacity >> SCHED_POWER_SHIFT;
> >>      else if (4 * max_capacity < (3 * (max_capacity + min_capacity)))
> >>              middle_capacity = (min_capacity + max_capacity)
> >>                              >> (SCHED_POWER_SHIFT+1);
> >
>