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Date: Thu, 9 Nov 2023 14:32:52 -0600
From: "Moger, Babu" <babu.moger@....com>
To: James Morse <james.morse@....com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: 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>,
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,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
dfustini@...libre.com, amitsinght@...vell.com
Subject: Re: [PATCH v7 07/24] x86/resctrl: Allow RMID allocation to be scoped
by CLOSID
Hi James,
On 10/25/23 13:03, 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>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@...itsu.com>
> Signed-off-by: James Morse <james.morse@....com>
Reviewed-by: Babu Moger <babu.moger@....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()
>
> Changes since v3:
> * Flipped conditions in alloc_rmid()
>
> Changes since v4:
> * Typo in comment
>
> Changes since v5:
> * Reworded two comments.
>
> Changes since v6:
> * Fixed a typo and some whitespace.
> ---
> arch/x86/kernel/cpu/resctrl/internal.h | 2 +-
> arch/x86/kernel/cpu/resctrl/monitor.c | 51 +++++++++++++++++------
> arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 2 +-
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 +-
> 4 files changed, 41 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> index 97ec24f91ac4..2f1d4f141dab 100644
> --- a/arch/x86/kernel/cpu/resctrl/internal.h
> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> @@ -545,7 +545,7 @@ 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 __exit rdt_put_mon_l3_config(struct rdt_resource *r);
> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index c02cf32cd17c..3c9343dffdf7 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -344,24 +344,49 @@ bool has_busy_rmid(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);
> +
> + 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, the two
> + * index values are always the same on every entry and thus the
> + * very first entry will be returned.
> + */
> + 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;
> + }
> +
> + 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 free 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))
> + return PTR_ERR(entry);
>
> - entry = list_first_entry(&rmid_free_lru,
> - struct rmid_entry, list);
> list_del(&entry->list);
> -
> return entry->rmid;
> }
>
> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index 65bee6f11015..d8f44113ed1f 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -777,7 +777,7 @@ 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 22dbdfe569a1..9864cb49d58c 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3300,7 +3300,7 @@ 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;
--
Thanks
Babu Moger
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