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

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Date:   Fri, 24 Mar 2023 11:35:08 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Pierre Gondois <pierre.gondois@....com>
Cc:     Yicong Yang <yangyicong@...wei.com>, gregkh@...uxfoundation.org,
        rafael@...nel.org, palmer@...osinc.com,
        linux-kernel@...r.kernel.org, prime.zeng@...ilicon.com,
        linuxarm@...wei.com, yangyicong@...ilicon.com
Subject: Re: [PATCH] cacheinfo: Fix LLC is not exported through sysfs

On Thu, Mar 23, 2023 at 06:58:53PM +0100, Pierre Gondois wrote:
> 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.
> >

IIUC this is for the case where arch register doesn't report the system level
cache. I wonder if it makes sense to fix the arch callback to deal with that
instead of here. I am fine either way, just checking as ideally it is
something populate_cache_leaves() is messing up.

[...]

> > @@ -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.)
>

Agreed, I prefer that as well.

-- 
Regards,
Sudeep