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

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Date:   Tue, 28 Mar 2023 09:45:30 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Yicong Yang <yangyicong@...wei.com>
Cc:     yangyicong@...ilicon.com, Pierre Gondois <pierre.gondois@....com>,
        gregkh@...uxfoundation.org, rafael@...nel.org, palmer@...osinc.com,
        linux-kernel@...r.kernel.org, prime.zeng@...ilicon.com,
        linuxarm@...wei.com
Subject: Re: [PATCH] cacheinfo: Fix LLC is not exported through sysfs

On Tue, Mar 28, 2023 at 04:15:17PM +0800, Yicong Yang wrote:
> On 2023/3/27 19:15, Sudeep Holla wrote:
> > On Mon, Mar 27, 2023 at 02:57:07PM +0800, Yicong Yang wrote:
> >> Hi Pierre and Sudeep,
> >>
> >> On 2023/3/24 19:35, Sudeep Holla wrote:
> >>> 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.
> >>>
> >>
> >> yes it's right, the LLC information is not provided by the CPU register and can
> >> only be retrieved from PPTT on my machine. Maybe fix the issue first, I don't
> >> know how to make arch callback handle this since arch_topology is also used
> >> other than arm64 which I'm not familiar with.
> >>
> > 
> > I was thinking of something like below.
> > 
> > --
> > Regards,
> > Sudeep
> > 
> > diff --git i/arch/arm64/kernel/cacheinfo.c w/arch/arm64/kernel/cacheinfo.c
> > index c307f69e9b55..4ef1033fe47e 100644
> > --- i/arch/arm64/kernel/cacheinfo.c
> > +++ w/arch/arm64/kernel/cacheinfo.c
> > @@ -79,12 +79,16 @@ int init_cache_level(unsigned int cpu)
> > 
> >  int populate_cache_leaves(unsigned int cpu)
> >  {
> > -       unsigned int level, idx;
> > +       unsigned int hw_lvl, level, idx;
> >         enum cache_type type;
> >         struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
> >         struct cacheinfo *this_leaf = this_cpu_ci->info_list;
> > 
> > -       for (idx = 0, level = 1; level <= this_cpu_ci->num_levels &&
> > +       for (hw_lvl = 0; hw_lvl <= MAX_CACHE_LEVEL; hw_lvl++)
> > +               if (CACHE_TYPE_NOCACHE == get_cache_type(hw_lvl + 1))
> > +                       break;
> > +
> 
> We totally skip the system level caches and leaving their ->level initialized
> as 0, then we still cannot get the correct infomation by the PPTT side since
> it uses the ->level to find the cache info:

Ah OK, in that case I fine with your approach, I assume few things wrong
when we reach the arch code.

-- 
Regards,
Sudeep