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SubjectRe: [PATCH v5 09/19] arch_topology: Use the last level cache information from the cacheinfo
Date


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.

>
> 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;
/*
* 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");
+ return false;
+ }

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

#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);

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

#ifdef CONFIG_OF
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