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Date: Mon, 14 Aug 2023 18:22:04 -0700
From: Fenghua Yu <fenghua.yu@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
<linux-kernel@...r.kernel.org>
CC: 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>,
<dfustini@...libre.com>
Subject: Re: [PATCH v5 05/24] x86/resctrl: Allow RMID allocation to be scoped
by CLOSID
Hi, James,
On 7/28/23 09:42, 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()
>
> Changes since v3:
> * Flipped conditions in alloc_rmid()
>
> Changes since v4:
> * Typo in comment
> ---
> 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 b48715bb8762..94749ee950dd 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 bd234b66dddf..de91ca781d9f 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -337,24 +337,49 @@ 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, these will
> + * always be the same meaning the compiler can reduce this loop
> + * to a single list_entry_first() call.
s/list_entry_first()/list_first_entry()/?
Seems the comment is not accurate because the loop is not really reduced
to a single list_first_entry() call. Getting itr_idx and cmp_idx and
comparing them are extra operations that list_first_entry() doesn't have.
Maybe change the second half comment to something like:
If the CLOSID is irrelevant on this architecture, the two index values
are always 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 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))
> + 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 aeadaeb5df9a..5ebd6e54c7f2 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 7c5cfb373d03..b97e119dbe46 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -3172,7 +3172,7 @@ 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.
-Fenghua
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