[External] Re: [PATCH v2 2/3] riscv: cacheinfo: initialize cacheinfo's level and type from ACPI PPTT

[yunhui cui]

Hi Sudeep,

On Mon, Apr 15, 2024 at 4:45 PM Sudeep Holla <sudeep.holla at arm.com> wrote:
>
> On Sun, Apr 14, 2024 at 10:58:25AM +0800, Yunhui Cui wrote:
> > Before cacheinfo can be built correctly, we need to initialize level
> > and type. Since RSIC-V currently does not have a register group that
> > describes cache-related attributes like ARM64, we cannot obtain them
> > directly, so now we obtain cache leaves from the ACPI PPTT table
> > (acpi_get_cache_info()) and set the cache type through split_levels.
> >
> > Suggested-by: Jeremy Linton <jeremy.linton at arm.com>
> > Suggested-by: Sudeep Holla <sudeep.holla at arm.com>
> > Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
> > ---
> >  arch/riscv/kernel/cacheinfo.c | 23 +++++++++++++++++++++++
> >  1 file changed, 23 insertions(+)
> >
> > diff --git a/arch/riscv/kernel/cacheinfo.c b/arch/riscv/kernel/cacheinfo.c
> > index 30a6878287ad..ece92aa404e3 100644
> > --- a/arch/riscv/kernel/cacheinfo.c
> > +++ b/arch/riscv/kernel/cacheinfo.c
> > @@ -6,6 +6,7 @@
> >  #include <linux/cpu.h>
> >  #include <linux/of.h>
> >  #include <asm/cacheinfo.h>
> > +#include <linux/acpi.h>
> >
> >  static struct riscv_cacheinfo_ops *rv_cache_ops;
> >
> > @@ -78,6 +79,28 @@ int populate_cache_leaves(unsigned int cpu)
> >       struct device_node *prev = NULL;
> >       int levels = 1, level = 1;
> >
> > +     if (!acpi_disabled) {
> > +             int ret, idx, fw_levels, split_levels;
> > +
> > +             ret = acpi_get_cache_info(cpu, &fw_levels, &split_levels);
> > +             if (ret)
> > +                     return ret;
> > +
> > +             /* must be set, so we can drop num_leaves assignment below */
>
> I intentionally added this above comment to check and drop the below statement
> if it is already set. Please check if the value is already set when we call
> into this function(which I think is the case).
>
> > +             this_cpu_ci->num_leaves = fw_levels + split_levels;

Uh,got it. I understand that there is no need to add this line:
"this_cpu_ci->num_leaves = fw_levels + split_levels; " , because in
the Master core first it will:
smp_prepare_cpus
     ->init_cpu_topology
          ->for_each_possible_cpu(cpu) {
                 fetch_cache_info(cpu); //num_leaves and num_levels will be set
Then store_cpu_topology->update_siblings_masks->detect_cache_attributes->populate_cache_leaves().

Slave core will follow the logic of smp_callin->store_cpu_topology().
It's the same after I tested it, so I plan to remove that line and
update V3, what do you think?

Thanks,
Yunhui