linux-kernel - Re: [PATCH v5 09/19] arch_topology: Use the last level cache information from the cacheinfo

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Date:   Fri, 1 Jul 2022 12:11:56 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Conor.Dooley@...rochip.com
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        atishp@...shpatra.org, atishp@...osinc.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        wangqing@...o.com, robh+dt@...nel.org, rafael@...nel.org,
        ionela.voinescu@....com, pierre.gondois@....com,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, gshan@...hat.com,
        Valentina.FernandezAlanis@...rochip.com
Subject: Re: [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@...rochip.com wrote:
> 
> 
> On 30/06/2022 21:21, Sudeep Holla wrote:
> > On Thu, Jun 30, 2022 at 08:13:55PM +0000, Conor.Dooley@...rochip.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