linux-kernel - Re: [PATCH] cacheinfo: Fix LLC is not exported through sysfs

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Message-ID: <7cca5e74-6626-1c8b-9309-47b9f5d4395f@arm.com>
Date:   Thu, 23 Mar 2023 18:58:53 +0100
From:   Pierre Gondois <pierre.gondois@....com>
To:     Yicong Yang <yangyicong@...wei.com>, gregkh@...uxfoundation.org,
        rafael@...nel.org, sudeep.holla@....com, palmer@...osinc.com,
        linux-kernel@...r.kernel.org
Cc:     prime.zeng@...ilicon.com, linuxarm@...wei.com,
        yangyicong@...ilicon.com
Subject: Re: [PATCH] cacheinfo: Fix LLC is not exported through sysfs

Hello Yicong,

FWIW, I think the patch is correct and I could reproduce the issue.

On 3/23/23 13:25, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@...ilicon.com>
> 
> After entering 6.3-rc1 the LLC cacheinfo is not exported on our ACPI
> based arm64 server. This is because the LLC cacheinfo is partly reset
> when secondary CPUs boot up. On arm64 the primary cpu will allocate
> and setup cacheinfo:
> init_cpu_topology()
>    for_each_possible_cpu()
>      fetch_cache_info() // Allocate cacheinfo and init levels
> detect_cache_attributes()
>    cache_shared_cpu_map_setup()
>      if (!last_level_cache_is_valid()) // not valid, setup LLC
>        cache_setup_properties() // setup LLC
> 
> On secondary CPU boot up:
> detect_cache_attributes()
>    populate_cache_leaves()
>      get_cache_type() // Get cache type from clidr_el1,
>                       // for LLC type=CACHE_TYPE_NOCACHE
>    cache_shared_cpu_map_setup()
>      if (!last_level_cache_is_valid()) // Valid and won't go to this branch,
>                                        // leave LLC's type=CACHE_TYPE_NOCACHE
> 
> The last_level_cache_is_valid() use cacheinfo->{attributes, fw_token} to
> test it's valid or not, but populate_cache_leaves() will only reset
> LLC's type, so we won't try to re-setup LLC's type and leave it
> CACHE_TYPE_NOCACHE and won't export it through sysfs.
> 
> This patch tries to fix this by not re-populating the cache leaves if
> the LLC is valid.
> 
> Fixes: 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> ---
>   drivers/base/cacheinfo.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> index f6573c335f4c..d65f169d36dd 100644
> --- a/drivers/base/cacheinfo.c
> +++ b/drivers/base/cacheinfo.c
> @@ -473,6 +473,13 @@ int detect_cache_attributes(unsigned int cpu)
>   		return ret;
>   
>   populate_leaves:
> +	/*
> +	 * If LLC is valid the cache leaves were already populated so just go to
> +	 * update the cpu map.
> +	 */
> +	if (last_level_cache_is_valid(cpu))
> +		goto update_cpu_map;
> +
>   	/*
>   	 * populate_cache_leaves() may completely setup the cache leaves and
>   	 * shared_cpu_map or it may leave it partially setup.
> @@ -481,6 +488,7 @@ int detect_cache_attributes(unsigned int cpu)
>   	if (ret)
>   		goto free_ci;
>   
> +update_cpu_map:

Maybe just a suggestion about the code itself,
it should be possible to replace the 'goto' by an 'if' condition.
(Similarly, the 'populate_leaves:' label could have been avoided.)


>   	/*
>   	 * For systems using DT for cache hierarchy, fw_token
>   	 * and shared_cpu_map will be set up here only if they are

Thanks for the fix,
Pierre