Re: [PATCH v3 05/19] x86/resctrl: Allow RMID allocation to be scoped by CLOSID

Ilpo Järvinen
2023-03-21T11:30:05Z

On Mon, 20 Mar 2023, James Morse wrote:

> MPAMs RMID values are not unique unless the CLOSID is considered as well.
>
> alloc_rmid() expects the RMID to be an independent number.
>
> Pass the CLOSID in to alloc_rmid(). Use this to compare indexes when
> allocating. If the CLOSID is not relevant to the index, this ends up
> comparing the free RMID with itself, and the first free entry will be
> used. With MPAM the CLOSID is included in the index, so this becomes a
> walk of the free RMID entries, until one that matches the supplied
> CLOSID is found.
>
> Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> Changes since v2;
> * Rephrased comment in resctrl_find_free_rmid() to describe this in terms of
> list_entry_first()
> * Rephrased comment above alloc_rmid()
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 2 +-
> arch/x86/kernel/cpu/resctrl/monitor.c | 54 +++++++++++++++++------
> arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 2 +-
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 +-
> 4 files changed, 43 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 47506e2afd59..e11d9ce943d3 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -535,7 +535,7 @@ void rdtgroup_pseudo_lock_remove(struct rdtgroup *rdtgrp);
> struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r);
> int closids_supported(void);
> void closid_free(int closid);
> -int alloc_rmid(void);
> +int alloc_rmid(u32 closid);
> void free_rmid(u32 closid, u32 rmid);
> int rdt_get_mon_l3_config(struct rdt_resource *r);
> bool __init rdt_cpu_has(int flag);
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 03a7d13dd653..ca58a433c668 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -337,25 +337,51 @@ bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
> return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;
> }
>
> -/*
> - * As of now the RMIDs allocation is global.
> - * However we keep track of which packages the RMIDs
> - * are used to optimize the limbo list management.
> - */
> -int alloc_rmid(void)
> +static struct rmid_entry *resctrl_find_free_rmid(u32 closid)
> {
> - struct rmid_entry *entry;
> -
> - lockdep_assert_held(&rdtgroup_mutex);
> + struct rmid_entry *itr;
> + u32 itr_idx, cmp_idx;
>
> if (list_empty(&rmid_free_lru))
> - return rmid_limbo_count ? -EBUSY : -ENOSPC;
> + return rmid_limbo_count ? ERR_PTR(-EBUSY) : ERR_PTR(-ENOSPC);
>
> - entry = list_first_entry(&rmid_free_lru,
> - struct rmid_entry, list);
> - list_del(&entry->list);
> + list_for_each_entry(itr, &rmid_free_lru, list) {
> + /*
> + * get the index of this free RMID, and the index it would need
> + * to be if it were used with this CLOSID.
> + * If the CLOSID is irrelevant on this architecture, these will
> + * always be the same meaning the compiler can reduce this loop
> + * to a single list_entry_first() call.
> + */
> + itr_idx = resctrl_arch_rmid_idx_encode(itr->closid, itr->rmid);
> + cmp_idx = resctrl_arch_rmid_idx_encode(closid, itr->rmid);
>
> - return entry->rmid;
> + if (itr_idx == cmp_idx)
> + return itr;
> + }
> +
> + return ERR_PTR(-ENOSPC);
> +}
> +
> +/*
> + * For MPAM the RMID value is not unique, and has to be considered with
> + * the CLOSID. The (CLOSID, RMID) pair is allocated on all domains, which
> + * allows all domains to be managed by a single limbo list.
> + * Each domain also has a rmid_busy_llc to reduce the work of the limbo handler.
> + */
> +int alloc_rmid(u32 closid)
> +{
> + struct rmid_entry *entry;
> +
> + lockdep_assert_held(&rdtgroup_mutex);
> +
> + entry = resctrl_find_free_rmid(closid);
> + if (!IS_ERR(entry)) {
> + list_del(&entry->list);
> + return entry->rmid;
> + }
> +
> + return PTR_ERR(entry);

Reverse the if condition to make this follow the normal error handling
pattern.

--
i.