[PATCH v2 06/12] ARM: mcpm: change max clusters to 4

[Nicolas Pitre]

On Tue, 15 Apr 2014, Haojian Zhuang wrote:

> On 11 April 2014 10:39, Nicolas Pitre <nicolas.pitre at linaro.org> wrote:
> > On Thu, 10 Apr 2014, Dave Martin wrote:
> >
> >> On Tue, Apr 08, 2014 at 04:00:46PM +0800, Haojian Zhuang wrote:
> >> > In order to support 4 clusters with 4 Cortex A15 Cores in each cluster,
> >> > enlarge maximum clusters from 2 to 4 in MCPM.
> >>
> >> CC Nico on mcpm patches please.  I'm happy to be CC'd as well.
> >
> > Indeed.
> >
> >> > Signed-off-by: Haojian Zhuang <haojian.zhuang at linaro.org>
> >> > ---
> >> >  arch/arm/include/asm/mcpm.h | 2 +-
> >> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >> >
> >> > diff --git a/arch/arm/include/asm/mcpm.h b/arch/arm/include/asm/mcpm.h
> >> > index 608516e..68f82cf 100644
> >> > --- a/arch/arm/include/asm/mcpm.h
> >> > +++ b/arch/arm/include/asm/mcpm.h
> >> > @@ -20,7 +20,7 @@
> >> >   * to consider dynamic allocation.
> >> >   */
> >> >  #define MAX_CPUS_PER_CLUSTER       4
> >> > -#define MAX_NR_CLUSTERS            2
> >> > +#define MAX_NR_CLUSTERS            4
> >>
> >> Because of the need for alignment to the biggest cacheline size in the
> >> system, the MCPM low-level locking structures consume a non-trivial
> >> amount of memory.
> >>
> >> Therefore, I'm not keen on the idea of simply increasing this #define
> >> every time a platform appears with a larger number of clusters.
> >> If hip04 is not built into the kernel, this just wastes memory.
> >>
> >> I'll leave it to Nico to decide whether we can increase the #define
> >> to 4 or whether this needs a proper fix now.  Ideally, we would have
> >> a way of choosing the maximum value required by the set of boards built
> >> into the kernel, or switch to dynamic allocation.
> >
> > I think we should go with the ability to select a maximum based on the
> > configured platforms. That could be as simple as having a
> > CONFIG_MCPM_QUAD_CLUSTER symbol to be selected by those platforms that
> > need it.
> >
> 
> I'll set MAX_NR_CLUSTERS from Kconfig.
> 
> If BIG_LITTLE isn't enabled & HIP04 is enabled, MAX_NR_CLUSTERS could
> be set to 4.
> Otherwise, it's always 2. Since there're only 16 A15 cores in HiP04.

No.

Please let's avoid cross dependencies for things that are conceptually 
unrelated.

Like I suggested, just create a CONFIG_MCPM_QUAD_CLUSTER symbol and 
select it from the HIP04 config.

For multi-platform kernels we must be able to support both BIG_LITTLE 
and HIP04 in the same config.  Whether or not the big.LITTLE code is 
activated can be decided at run time.


Nicolas