RE: [PATCH v2 05/18] x86/resctrl: Allow RMID allocation to be scoped by CLOSID

[Yu, Fenghua]

Hi, James,

> 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@xxxxxxxxxxx>
> Signed-off-by: James Morse <james.morse@xxxxxxx>
> ---
>  arch/x86/kernel/cpu/resctrl/internal.h    |  2 +-
>  arch/x86/kernel/cpu/resctrl/monitor.c     | 44 ++++++++++++++++++-----
>  arch/x86/kernel/cpu/resctrl/pseudo_lock.c |  2 +-
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c    |  2 +-
>  4 files changed, 38 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h
> b/arch/x86/kernel/cpu/resctrl/internal.h
> index af71401c57e2..013c8fc9fd28 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -510,7 +510,7 @@ 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);  void mon_event_count(void
> *info); diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
> b/arch/x86/kernel/cpu/resctrl/monitor.c
> index dbae380e3d1c..347be3767241 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -301,25 +301,51 @@ bool has_busy_rmid(struct rdt_resource *r, struct
> rdt_domain *d)
>  	return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;  }
> 
> +static struct rmid_entry *resctrl_find_free_rmid(u32 closid) {
> +	struct rmid_entry *itr;
> +	u32 itr_idx, cmp_idx;
> +
> +	if (list_empty(&rmid_free_lru))
> +		return rmid_limbo_count ? ERR_PTR(-EBUSY) : ERR_PTR(-
> ENOSPC);
> +
> +	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. Otherwise they will only match if this
> +		 * RMID can be used with this CLOSID.
> +		 */
> +		itr_idx = resctrl_arch_rmid_idx_encode(itr->closid, itr->rmid);
> +		cmp_idx = resctrl_arch_rmid_idx_encode(closid, itr->rmid);
> +
> +		if (itr_idx == cmp_idx)
> +			return itr;

Finding free rmid may be called frequently depending on usage.

It would be better to have a simpler and faster arch helper that finds the itr on x86.
Something like:
struct rmid_entry *resctrl_arch_rmid_matchd(u32 ignored, u32 ignored)
{
	return list_entry_first(resctrl_free_lru, itr, list);
}

Arm64 implements the complex case going through the rmid_free_lru list in the patch.

> +	}
> +
> +	return ERR_PTR(-ENOSPC);
> +}
> +
>  /*
> - * As of now the RMIDs allocation is global.
> + * As of now the RMIDs allocation is the same in each domain.
>   * However we keep track of which packages the RMIDs
>   * are used to optimize the limbo list management.
> + * The closid is ignored on x86.
>   */
> -int alloc_rmid(void)
> +int alloc_rmid(u32 closid)
>  {
>  	struct rmid_entry *entry;
> 
>  	lockdep_assert_held(&rdtgroup_mutex);
> 
> -	if (list_empty(&rmid_free_lru))
> -		return rmid_limbo_count ? -EBUSY : -ENOSPC;
> +	entry = resctrl_find_free_rmid(closid);
> +	if (!IS_ERR(entry)) {
> +		list_del(&entry->list);
> +		return entry->rmid;
> +	}
> 
> -	entry = list_first_entry(&rmid_free_lru,
> -				 struct rmid_entry, list);
> -	list_del(&entry->list);
> -
> -	return entry->rmid;
> +	return PTR_ERR(entry);
>  }
> 
>  static void add_rmid_to_limbo(struct rmid_entry *entry) diff --git
> a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index c51932516965..3b724a40d3a2 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -763,7 +763,7 @@ int rdtgroup_locksetup_exit(struct rdtgroup *rdtgrp)
>  	int ret;
> 
>  	if (rdt_mon_capable) {
> -		ret = alloc_rmid();
> +		ret = alloc_rmid(rdtgrp->closid);
>  		if (ret < 0) {
>  			rdt_last_cmd_puts("Out of RMIDs\n");
>  			return ret;
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index c67083a8a5f5..ac88610a6946 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -2875,7 +2875,7 @@ static int mkdir_rdt_prepare_rmid_alloc(struct
> rdtgroup *rdtgrp)
>  	if (!rdt_mon_capable)
>  		return 0;
> 
> -	ret = alloc_rmid();
> +	ret = alloc_rmid(rdtgrp->closid);
>  	if (ret < 0) {
>  		rdt_last_cmd_puts("Out of RMIDs\n");
>  		return ret;
> --
> 2.30.2

Thanks.

-Fenghua