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

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Date:   Tue, 21 Mar 2023 13:29:48 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     James Morse <james.morse@....com>
cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        shameerali.kolothum.thodi@...wei.com,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        xingxin.hx@...nanolis.org, baolin.wang@...ux.alibaba.com,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com
Subject: Re: [PATCH v3 05/19] x86/resctrl: Allow RMID allocation to be scoped
 by CLOSID

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@...itsu.com>
> Signed-off-by: James Morse <james.morse@....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.