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SubjectRe: [PATCH v5 09/19] arch_topology: Use the last level cache information from the cacheinfo
On Thu, Jun 30, 2022 at 10:07:49PM +0000, Conor.Dooley@microchip.com wrote:
>
>
> On 30/06/2022 21:21, Sudeep Holla wrote:
> > On Thu, Jun 30, 2022 at 08:13:55PM +0000, Conor.Dooley@microchip.com wrote:
> >>
> >> I didn't have the time to go digging into things, but the following
> >> macro looked odd:
> >> #define per_cpu_cacheinfo_idx(cpu, idx) \
> >> (per_cpu_cacheinfo(cpu) + (idx))
> >> Maybe it is just badly named, but is this getting the per_cpu_cacheinfo
> >> and then incrementing intentionally, or is it meant to get the
> >> per_cpu_cacheinfo of cpu + idx?
> >
> > OK, basically per_cpu_cacheinfo(cpu) get the information for a cpu
> > while per_cpu_cacheinfo_idx(cpu, idx) will fetch the information for a
> > given cpu and given index within the cpu. So we are incrementing the
> > pointer by the index. These work just fine on arm64 platform.
>
> Right, that's what I figured but wanted to be sure.
>

OK

> >
> > Not sure if compiler is optimising something as I still can't understand
> > how we can end up with valid llc but fw_token as NULL.
> See idk about that. The following fails to boot.
> index 167abfa6f37d..9d45c37fb004 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -36,6 +36,8 @@ struct cpu_cacheinfo *get_cpu_cacheinfo(unsigned int cpu)
> static inline bool cache_leaves_are_shared(struct cacheinfo *this_leaf,
> struct cacheinfo *sib_leaf)
> {
> + if (!this_leaf || !sib_leaf)
> + return false;

Did you hit this ?

> /*
> * For non DT/ACPI systems, assume unique level 1 caches,
> * system-wide shared caches for all other levels. This will be used
> @@ -74,8 +76,12 @@ bool last_level_cache_is_shared(unsigned int cpu_x, unsigned int cpu_y)
>
> llc_x = per_cpu_cacheinfo_idx(cpu_x, cache_leaves(cpu_x) - 1);
> llc_y = per_cpu_cacheinfo_idx(cpu_y, cache_leaves(cpu_y) - 1);
> + if (!llc_x || !llc_y){
> + printk("llc was null\n");

Or this ?

> + return false;
> + }
>
> - return cache_leaves_are_shared(llc_x, llc_y);
> + return false; //cache_leaves_are_shared(llc_x, llc_y);

Even the above change fails to boot ? Coz you are always returning false here
too.

> }
>
> #ifdef CONFIG_OF
>
> and this boots:
>
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index 167abfa6f37d..01900908fe31 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -36,6 +36,8 @@ struct cpu_cacheinfo *get_cpu_cacheinfo(unsigned int cpu)
> static inline bool cache_leaves_are_shared(struct cacheinfo *this_leaf,
> struct cacheinfo *sib_leaf)
> {
> + if (!this_leaf || !sib_leaf)
> + return false;
> /*
> * For non DT/ACPI systems, assume unique level 1 caches,
> * system-wide shared caches for all other levels. This will be used
> @@ -75,7 +77,7 @@ bool last_level_cache_is_shared(unsigned int cpu_x, unsigned int cpu_y)
> llc_x = per_cpu_cacheinfo_idx(cpu_x, cache_leaves(cpu_x) - 1);
> llc_y = per_cpu_cacheinfo_idx(cpu_y, cache_leaves(cpu_y) - 1);
>

You are just missing the checks for llc_x and llc_y and it works which
means llc_x and llc_y is where things are going wrong.

--
Regards,
Sudeep

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