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Message-ID: <e0320c8d-8bdc-4d8f-a165-b3637730163d@intel.com>
Date: Tue, 3 Jun 2025 20:42:36 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghuay@...dia.com>, "Maciej
Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
<Dave.Martin@....com>, Anil Keshavamurthy <anil.s.keshavamurthy@...el.com>,
Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
<patches@...ts.linux.dev>
Subject: Re: [PATCH v5 13/29] x86,fs/resctrl: Handle events that can be read
from any CPU
Hi Tony,
On 5/21/25 3:50 PM, Tony Luck wrote:
> Resctrl file system code was built with the assumption that monitor
> events can only be read from a CPU in the cpumask_t set for each
> domain.
>
> This was true for x86 events accessed with an MSR interface, but may
> not be true for other access methods such as MMIO.
>
> Add a flag to struct mon_evt to indicate which events can be read on
> any CPU.
Since struct mon_evt is per-event, how about:
"Add a flag to struct mon_evt to indicate if the event can be read on
any CPU."
>
> Architecture uses resctrl_enable_mon_event() to enable an event and
> set the flag appropriately.
>
> Bypass all the smp_call*() code for events that can be read on any CPU
> and call mon_event_count() directly from mon_event_read().
>
> Skip checks in __mon_event_count() that the read is being done from
> a CPU in the correct domain or cache scope.
>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
> include/linux/resctrl.h | 2 +-
> fs/resctrl/internal.h | 2 ++
> arch/x86/kernel/cpu/resctrl/core.c | 6 +++---
> fs/resctrl/ctrlmondata.c | 7 ++++++-
> fs/resctrl/monitor.c | 26 ++++++++++++++++++++------
> 5 files changed, 32 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index b7a4c7bf4feb..9aab3d78005a 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -377,7 +377,7 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
> u32 resctrl_arch_system_num_rmid_idx(void);
> int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
>
> -void resctrl_enable_mon_event(enum resctrl_event_id evtid);
> +void resctrl_enable_mon_event(enum resctrl_event_id evtid, bool any_cpu);
>
> bool resctrl_is_mon_event_enabled(enum resctrl_event_id evt);
>
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index 085a2ee1922f..eb6e92d1ab15 100644
> --- a/fs/resctrl/internal.h
> +++ b/fs/resctrl/internal.h
> @@ -57,6 +57,7 @@ static inline struct rdt_fs_context *rdt_fc2context(struct fs_context *fc)
> * @rid: index of the resource for this event
> * @name: name of the event
> * @configurable: true if the event is configurable
> + * @any_cpu: true if the event can be read from any CPU
> * @enabled: true if the event is enabled
> */
> struct mon_evt {
> @@ -64,6 +65,7 @@ struct mon_evt {
> enum resctrl_res_level rid;
> char *name;
> bool configurable;
> + bool any_cpu;
> bool enabled;
> };
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index b39537658618..5d9a024ce4b0 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -880,15 +880,15 @@ static __init bool get_rdt_mon_resources(void)
> bool ret = false;
>
> if (rdt_cpu_has(X86_FEATURE_CQM_OCCUP_LLC)) {
> - resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID);
> + resctrl_enable_mon_event(QOS_L3_OCCUP_EVENT_ID, false);
> ret = true;
> }
> if (rdt_cpu_has(X86_FEATURE_CQM_MBM_TOTAL)) {
> - resctrl_enable_mon_event(QOS_L3_MBM_TOTAL_EVENT_ID);
> + resctrl_enable_mon_event(QOS_L3_MBM_TOTAL_EVENT_ID, false);
> ret = true;
> }
> if (rdt_cpu_has(X86_FEATURE_CQM_MBM_LOCAL)) {
> - resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID);
> + resctrl_enable_mon_event(QOS_L3_MBM_LOCAL_EVENT_ID, false);
> ret = true;
> }
>
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index dcde27f6f2ec..1337716f59c8 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -569,6 +569,11 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
> return;
> }
>
> + if (evt->any_cpu) {
> + mon_event_count(rr);
> + goto done;
Please see earlier details about goto in resctrl. This can be "out_ctx_free".
> + }
> +
> cpu = cpumask_any_housekeeping(cpumask, RESCTRL_PICK_ANY_CPU);
>
> /*
> @@ -581,7 +586,7 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
> smp_call_function_any(cpumask, mon_event_count, rr, 1);
> else
> smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
> -
> +done:
> resctrl_arch_mon_ctx_free(r, evt->evtid, rr->arch_mon_ctx);
> }
>
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 3cfd1bf1845e..e6e3be990638 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -356,9 +356,24 @@ static struct mbm_state *get_mbm_state(struct rdt_l3_mon_domain *d, u32 closid,
> return states ? &states[idx] : NULL;
> }
>
> +static bool cpu_on_wrong_domain(struct rmid_read *rr)
> +{
> + cpumask_t *mask;
> +
> + if (rr->evt->any_cpu)
> + return false;
> +
> + /*
> + * When reading from a specific domain the CPU must be in that
> + * domain. Otherwise the CPU must be one that shares the cache.
> + */
> + mask = rr->d ? &rr->d->hdr.cpu_mask : &rr->ci->shared_cpu_map;
> +
> + return !cpumask_test_cpu(smp_processor_id(), mask);
> +}
I find double-negatives can trip people up. Having function name contain
"wrong" while also returning "!" can be confusing. I think this will be simpler
if it is a straight-forward utility, for example, "cpu_on_correct_domain()"?
Maybe even "current_cpu_on_correct_domain()" to be explicit about which CPU
is being checked.
> +
> static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
> {
> - int cpu = smp_processor_id();
> struct rdt_l3_mon_domain *d;
> struct mbm_state *m;
> int err, ret;
> @@ -373,8 +388,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
> }
>
> if (rr->d) {
> - /* Reading a single domain, must be on a CPU in that domain. */
> - if (!cpumask_test_cpu(cpu, &rr->d->hdr.cpu_mask))
> + if (cpu_on_wrong_domain(rr))
> return -EINVAL;
> rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid,
> rr->evt->evtid, &tval, rr->arch_mon_ctx);
> @@ -386,8 +400,7 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
> return 0;
> }
>
> - /* Summing domains that share a cache, must be on a CPU for that cache. */
> - if (!cpumask_test_cpu(cpu, &rr->ci->shared_cpu_map))
> + if (cpu_on_wrong_domain(rr))
> return -EINVAL;
>
> /*
> @@ -865,7 +878,7 @@ struct mon_evt mon_event_all[QOS_NUM_EVENTS] = {
> },
> };
>
> -void resctrl_enable_mon_event(enum resctrl_event_id evtid)
> +void resctrl_enable_mon_event(enum resctrl_event_id evtid, bool any_cpu)
> {
> if (WARN_ON_ONCE(evtid >= QOS_NUM_EVENTS))
> return;
> @@ -874,6 +887,7 @@ void resctrl_enable_mon_event(enum resctrl_event_id evtid)
> return;
> }
>
> + mon_event_all[evtid].any_cpu = any_cpu;
> mon_event_all[evtid].enabled = true;
> }
>
Reinette
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