linux-kernel - Re: [PATCH v6 1/8] x86/resctrl: Prepare for new domain scope

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Date:   Fri, 29 Sep 2023 14:09:42 +0200
From:   Peter Newman <peternewman@...gle.com>
To:     Tony Luck <tony.luck@...el.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, x86@...nel.org,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Babu Moger <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v6 1/8] x86/resctrl: Prepare for new domain scope

Hi Tony,

On Thu, Sep 28, 2023 at 9:14 PM Tony Luck <tony.luck@...el.com> wrote:
>
> Resctrl resources operate on subsets of CPUs in the system with the
> defining attribute of each subset being an instance of a particular
> level of cache. E.g. all CPUs sharing an L3 cache would be part of the
> same domain.
>
> In preparation for features that are scoped at the NUMA node level
> change the code from explicit references to "cache_level" to a more
> generic scope. At this point the only options for this scope are groups
> of CPUs that share an L2 cache or L3 cache.
>
> Provide a more detailed warning message if a domain id cannot be found
> when adding a CPU. Just check and silent return if the domain id can't
> be found when removing a CPU.
>
> No functional change.

I see a number of diagnostic checks added below. Are you sure there's
no functional change?


> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index 8f559eeae08e..8c5f932bc00b 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -292,10 +292,14 @@ static void pseudo_lock_region_clear(struct pseudo_lock_region *plr)
>   */
>  static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>  {
> +       int scope = plr->s->res->scope;
>         struct cpu_cacheinfo *ci;
>         int ret;
>         int i;
>
> +       if (WARN_ON_ONCE(scope != RESCTRL_L2_CACHE && scope != RESCTRL_L3_CACHE))
> +               return -ENODEV;

Functional change?


> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 725344048f85..1cf2b36f5bf8 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1345,10 +1345,13 @@ unsigned int rdtgroup_cbm_to_size(struct rdt_resource *r,
>         unsigned int size = 0;
>         int num_b, i;
>
> +       if (WARN_ON_ONCE(r->scope != RESCTRL_L2_CACHE && r->scope != RESCTRL_L3_CACHE))
> +               return -EINVAL;

This function returns unsigned int. That's a huge region!

-Peter