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SubjectRe: [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@hisilicon.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

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