Date:	Fri, 29 Apr 2016 14:32:13 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
To:	David Carrillo-Cisneros <davidcc@...gle.com>
cc:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Stephane Eranian <eranian@...gle.com>,
	Paul Turner <pjt@...gle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/32] perf/x86/intel/cqm: integrate CQM cgroups with
 scheduler



On Fri, 29 Apr 2016, David Carrillo-Cisneros wrote:

> if __intel_cqm_no_event_sched_in does nothing, the PQR_ASSOC msr is
> still updated if state->rmid != state->next_rmid  in __pqr_update,

But due to 2 and 3 below they are equal ?


> even if next_rmid_mode == PQR_RMID_MODE_NOEVENT .
>
> On Fri, Apr 29, 2016 at 2:01 PM, Vikas Shivappa
> <vikas.shivappa@...ux.intel.com> wrote:
>>
>>
>> On Fri, 29 Apr 2016, David Carrillo-Cisneros wrote:
>>
>>> Not sure I see the problem you point here. In step 3, PQR_ASSOC is
>>> updated with RMID1, __pqr_update is the one called using the scheduler
>>> hook, right after perf sched_in .
>>>
>>> On Fri, Apr 29, 2016 at 1:25 PM, Vikas Shivappa
>>> <vikas.shivappa@...ux.intel.com> wrote:
>>>>
>>>>
>>>>
>>>> On Thu, 28 Apr 2016, David Carrillo-Cisneros wrote:
>>>>
>>>>> Allow monitored cgroups to update the PQR MSR during task switch even
>>>>> without an associated perf_event.
>>>>>
>>>>> The package RMID for the current monr associated with a monitored
>>>>> cgroup is written to hw during task switch (after perf_events is run)
>>>>> if perf_event did not write a RMID for an event.
>>>>>
>>>>> perf_event and any other caller of pqr_cache_update_rmid can update the
>>>>> CPU's RMID using one of two modes:
>>>>>  - PQR_RMID_MODE_NOEVENT: A RMID that do not correspond to an event.
>>>>>    e.g. the RMID of the root pmonr when no event is scheduled.
>>>>>  - PQR_RMID_MODE_EVENT:   A RMID used by an event. Set during pmu::add
>>>>> unset on pmu::del. This mode prevents from using a non-event
>>>>> cgroup RMID.
>>>>>
>>>>> This patch also introduces caching of writes to PQR MSR within the
>>>>> per-pcu
>>>>> pqr state variable. This interface to update RMIDs and CLOSIDs will be
>>>>> also utilized in upcoming versions of Intel's MBM and CAT drivers.
>>>>>
>>>>> Reviewed-by: Stephane Eranian <eranian@...gle.com>
>>>>> Signed-off-by: David Carrillo-Cisneros <davidcc@...gle.com>
>>>>> ---
>>>>> arch/x86/events/intel/cqm.c       | 65
>>>>> +++++++++++++++++++++++++++++----------
>>>>> arch/x86/events/intel/cqm.h       |  2 --
>>>>> arch/x86/include/asm/pqr_common.h | 53 +++++++++++++++++++++++++++----
>>>>> arch/x86/kernel/cpu/pqr_common.c  | 46 +++++++++++++++++++++++----
>>>>> 4 files changed, 135 insertions(+), 31 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/events/intel/cqm.c b/arch/x86/events/intel/cqm.c
>>>>> index daf9fdf..4ece0a4 100644
>>>>> --- a/arch/x86/events/intel/cqm.c
>>>>> +++ b/arch/x86/events/intel/cqm.c
>>>>> @@ -198,19 +198,6 @@ static inline int cqm_prmid_update(struct prmid
>>>>> *prmid)
>>>>>         return __cqm_prmid_update(prmid, __rmid_min_update_time);
>>>>> }
>>>>>
>>>>> -/*
>>>>> - * Updates caller cpu's cache.
>>>>> - */
>>>>> -static inline void __update_pqr_prmid(struct prmid *prmid)
>>>>> -{
>>>>> -       struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
>>>>> -
>>>>> -       if (state->rmid == prmid->rmid)
>>>>> -               return;
>>>>> -       state->rmid = prmid->rmid;
>>>>> -       wrmsr(MSR_IA32_PQR_ASSOC, prmid->rmid, state->closid);
>>>>> -}
>>>>> -
>>>>> static inline bool __valid_pkg_id(u16 pkg_id)
>>>>> {
>>>>>         return pkg_id < PQR_MAX_NR_PKGS;
>>>>> @@ -2531,12 +2518,11 @@ static inline bool cqm_group_leader(struct
>>>>> perf_event *event)
>>>>> static inline void __intel_cqm_event_start(
>>>>>         struct perf_event *event, union prmid_summary summary)
>>>>> {
>>>>> -       u16 pkg_id = topology_physical_package_id(smp_processor_id());
>>>>>         if (!(event->hw.state & PERF_HES_STOPPED))
>>>>>                 return;
>>>>> -
>>>>>         event->hw.state &= ~PERF_HES_STOPPED;
>>>>> -       __update_pqr_prmid(__prmid_from_rmid(pkg_id,
>>>>> summary.sched_rmid));
>>>>> +
>>>>> +       pqr_cache_update_rmid(summary.sched_rmid, PQR_RMID_MODE_EVENT);
>>>>> }
>>>>>
>>>>> static void intel_cqm_event_start(struct perf_event *event, int mode)
>>>>> @@ -2566,7 +2552,7 @@ static void intel_cqm_event_stop(struct perf_event
>>>>> *event, int mode)
>>>>>         /* Occupancy of CQM events is obtained at read. No need to read
>>>>>          * when event is stopped since read on inactive cpus succeed.
>>>>>          */
>>>>> -       __update_pqr_prmid(__prmid_from_rmid(pkg_id,
>>>>> summary.sched_rmid));
>>>>> +       pqr_cache_update_rmid(summary.sched_rmid,
>>>>> PQR_RMID_MODE_NOEVENT);
>>>>> }
>>>>>
>>>>> static int intel_cqm_event_add(struct perf_event *event, int mode)
>>>>> @@ -2977,6 +2963,8 @@ static void intel_cqm_cpu_starting(unsigned int
>>>>> cpu)
>>>>>
>>>>>         state->rmid = 0;
>>>>>         state->closid = 0;
>>>>> +       state->next_rmid = 0;
>>>>> +       state->next_closid = 0;
>>>>>
>>>>>         /* XXX: lock */
>>>>>         /* XXX: Make sure this case is handled when hotplug happens. */
>>>>> @@ -3152,6 +3140,12 @@ static int __init intel_cqm_init(void)
>>>>>         pr_info("Intel CQM monitoring enabled with at least %u rmids per
>>>>> package.\n",
>>>>>                 min_max_rmid + 1);
>>>>>
>>>>> +       /* Make sure pqr_common_enable_key is enabled after
>>>>> +        * cqm_initialized_key.
>>>>> +        */
>>>>> +       barrier();
>>>>> +
>>>>> +       static_branch_enable(&pqr_common_enable_key);
>>>>>         return ret;
>>>>>
>>>>> error_init_mutex:
>>>>> @@ -3163,4 +3157,41 @@ error:
>>>>>         return ret;
>>>>> }
>>>>>
>>>>> +/* Schedule task without a CQM perf_event. */
>>>>> +inline void __intel_cqm_no_event_sched_in(void)
>>>>> +{
>>>>> +#ifdef CONFIG_CGROUP_PERF
>>>>> +       struct monr *monr;
>>>>> +       struct pmonr *pmonr;
>>>>> +       union prmid_summary summary;
>>>>> +       u16 pkg_id = topology_physical_package_id(smp_processor_id());
>>>>> +       struct pmonr *root_pmonr = monr_hrchy_root->pmonrs[pkg_id];
>>>>> +
>>>>> +       /* Assume CQM enabled is likely given that PQR is enabled. */
>>>>> +       if (!static_branch_likely(&cqm_initialized_key))
>>>>> +               return;
>>>>> +
>>>>> +       /* Safe to call from_task since we are in scheduler lock. */
>>>>> +       monr = monr_from_perf_cgroup(perf_cgroup_from_task(current,
>>>>> NULL));
>>>>> +       pmonr = monr->pmonrs[pkg_id];
>>>>> +
>>>>> +       /* Utilize most up to date pmonr summary. */
>>>>> +       monr_hrchy_get_next_prmid_summary(pmonr);
>>>>> +       summary.value = atomic64_read(&pmonr->prmid_summary_atomic);
>>>>> +
>>>>> +       if (!prmid_summary__is_mon_active(summary))
>>>>> +               goto no_rmid;
>>>>> +
>>>>> +       if (WARN_ON_ONCE(!__valid_rmid(pkg_id, summary.sched_rmid)))
>>>>> +               goto no_rmid;
>>>>> +
>>>>> +       pqr_cache_update_rmid(summary.sched_rmid,
>>>>> PQR_RMID_MODE_NOEVENT);
>>>>> +       return;
>>>>> +
>>>>> +no_rmid:
>>>>> +       summary.value =
>>>>> atomic64_read(&root_pmonr->prmid_summary_atomic);
>>>>> +       pqr_cache_update_rmid(summary.sched_rmid,
>>>>> PQR_RMID_MODE_NOEVENT);
>>>>> +#endif
>>>>> +}
>>>>> +
>>>>> device_initcall(intel_cqm_init);
>>>>> diff --git a/arch/x86/events/intel/cqm.h b/arch/x86/events/intel/cqm.h
>>>>> index 0f3da94..e1f8bd0 100644
>>>>> --- a/arch/x86/events/intel/cqm.h
>>>>> +++ b/arch/x86/events/intel/cqm.h
>>>>> @@ -82,8 +82,6 @@ union prmid_summary {
>>>>>         };
>>>>> };
>>>>>
>>>>> -# define INVALID_RMID (-1)
>>>>> -
>>>>> /* A pmonr in (U)state has no sched_rmid, read_rmid can be 0 or
>>>>> INVALID_RMID
>>>>>  * depending on whether monitoring is active or not.
>>>>>  */
>>>>> diff --git a/arch/x86/include/asm/pqr_common.h
>>>>> b/arch/x86/include/asm/pqr_common.h
>>>>> index f770637..abbb235 100644
>>>>> --- a/arch/x86/include/asm/pqr_common.h
>>>>> +++ b/arch/x86/include/asm/pqr_common.h
>>>>> @@ -3,31 +3,72 @@
>>>>>
>>>>> #if defined(CONFIG_INTEL_RDT)
>>>>>
>>>>> +#include <linux/jump_label.h>
>>>>> #include <linux/types.h>
>>>>> #include <asm/percpu.h>
>>>>> +#include <asm/msr.h>
>>>>>
>>>>> #define MSR_IA32_PQR_ASSOC      0x0c8f
>>>>> +#define INVALID_RMID           (-1)
>>>>> +#define INVALID_CLOSID         (-1)
>>>>> +
>>>>> +
>>>>> +extern struct static_key_false pqr_common_enable_key;
>>>>> +
>>>>> +enum intel_pqr_rmid_mode {
>>>>> +       /* RMID has no perf_event associated. */
>>>>> +       PQR_RMID_MODE_NOEVENT = 0,
>>>>> +       /* RMID has a perf_event associated. */
>>>>> +       PQR_RMID_MODE_EVENT
>>>>> +};
>>>>>
>>>>> /**
>>>>>  * struct intel_pqr_state - State cache for the PQR MSR
>>>>> - * @rmid:              The cached Resource Monitoring ID
>>>>> - * @closid:            The cached Class Of Service ID
>>>>> + * @rmid:              Last rmid written to hw.
>>>>> + * @next_rmid:         Next rmid to write to hw.
>>>>> + * @next_rmid_mode:    Next rmid's mode.
>>>>> + * @closid:            The current Class Of Service ID
>>>>> + * @next_closid:       The Class Of Service ID to use.
>>>>>  *
>>>>>  * The upper 32 bits of MSR_IA32_PQR_ASSOC contain closid and the
>>>>>  * lower 10 bits rmid. The update to MSR_IA32_PQR_ASSOC always
>>>>>  * contains both parts, so we need to cache them.
>>>>>  *
>>>>> - * The cache also helps to avoid pointless updates if the value does
>>>>> - * not change.
>>>>> + * The cache also helps to avoid pointless updates if the value does
>>>>> not
>>>>> + * change. It also keeps track of the type of RMID set (event vs no
>>>>> event)
>>>>> + * used to determine when a cgroup RMID is required.
>>>>>  */
>>>>> struct intel_pqr_state {
>>>>> -       u32                     rmid;
>>>>> -       u32                     closid;
>>>>> +       u32                             rmid;
>>>>> +       u32                             next_rmid;
>>>>> +       enum intel_pqr_rmid_mode        next_rmid_mode;
>>>>> +       u32                             closid;
>>>>> +       u32                             next_closid;
>>>>> };
>>>>>
>>>>> DECLARE_PER_CPU(struct intel_pqr_state, pqr_state);
>>>>>
>>>>> #define PQR_MAX_NR_PKGS         8
>>>>>
>>>>> +void __pqr_update(void);
>>>>> +
>>>>> +inline void __intel_cqm_no_event_sched_in(void);
>>>>> +
>>>>> +inline void pqr_cache_update_rmid(u32 rmid, enum intel_pqr_rmid_mode
>>>>> mode);
>>>>> +
>>>>> +inline void pqr_cache_update_closid(u32 closid);
>>>>> +
>>>>> +static inline void pqr_update(void)
>>>>> +{
>>>>> +       if (static_branch_unlikely(&pqr_common_enable_key))
>>>>> +               __pqr_update();
>>>>> +}
>>>>> +
>>>>> +#else
>>>>> +
>>>>> +static inline void pqr_update(void)
>>>>> +{
>>>>> +}
>>>>> +
>>>>> #endif
>>>>> #endif
>>>>> diff --git a/arch/x86/kernel/cpu/pqr_common.c
>>>>> b/arch/x86/kernel/cpu/pqr_common.c
>>>>> index 9eff5d9..d91c127 100644
>>>>> --- a/arch/x86/kernel/cpu/pqr_common.c
>>>>> +++ b/arch/x86/kernel/cpu/pqr_common.c
>>>>> @@ -1,9 +1,43 @@
>>>>> #include <asm/pqr_common.h>
>>>>>
>>>>> -/*
>>>>> - * The cached intel_pqr_state is strictly per CPU and can never be
>>>>> - * updated from a remote CPU. Both functions which modify the state
>>>>> - * (intel_cqm_event_start and intel_cqm_event_stop) are called with
>>>>> - * interrupts disabled, which is sufficient for the protection.
>>>>> - */
>>>>> DEFINE_PER_CPU(struct intel_pqr_state, pqr_state);
>>>>> +
>>>>> +DEFINE_STATIC_KEY_FALSE(pqr_common_enable_key);
>>>>> +
>>>>> +inline void pqr_cache_update_rmid(u32 rmid, enum intel_pqr_rmid_mode
>>>>> mode)
>>>>> +{
>>>>> +       struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
>>>>> +
>>>>> +       state->next_rmid_mode = mode;
>>>>> +       state->next_rmid = rmid;
>>>>> +}
>>>>> +
>>>>> +inline void pqr_cache_update_closid(u32 closid)
>>>>> +{
>>>>> +       struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
>>>>> +
>>>>> +       state->next_closid = closid;
>>>>> +}
>>>>> +
>>>>> +/* Update hw's RMID using cgroup's if perf_event did not.
>>>>> + * Sync pqr cache with MSR.
>>>>> + */
>>>>> +inline void __pqr_update(void)
>>>>> +{
>>>>> +       struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
>>>>> +
>>>>> +       /* If perf_event has set a next_rmid that is used, do not try
>>>>> +        * to obtain another one from current task.
>>>>> +        */
>>>>> +       if (state->next_rmid_mode == PQR_RMID_MODE_NOEVENT)
>>>>> +               __intel_cqm_no_event_sched_in();
>>>>
>>>>
>>>>
>>>> if perf_cgroup is not defined then the state is not updated here so the
>>>> state might have state->rmid might have IDs ?
>>>>
>>>> 1.event1 for PID1 has RMID1,
>>>> 2.perf sched_in - state->next_rmid = rmid1
>>>> 3.pqr_update - state->rmid = rmid1
>>>> 4.sched_out - write PQR_NOEVENT -
>>>> 5.next switch_to - state->rmid not reset nothing changes (when no
>>>> perf_cgroup) ?
>>
>>
>> Between 4 and 5 say event1 is dead. Basically on the next context switch(#5)
>> if perf sched_in wasnt called the PQR still has RMID1.
>>
>> When you have perf_cgroup you call the __intel_cqm_no_event.. then it sees
>> if there is continuous monitoring or you set the next_rmid to 0- but all the
>> code there is inside #ifdef PERF_CGROUP, so without cgroup its never reset
>> to zero ?
>>
>>
>>
>>>>
>>>>
>>>>> +
>>>>> +       /* __intel_cqm_no_event_sched_in might have changed next_rmid.
>>>>> */
>>>>> +       if (state->rmid == state->next_rmid &&
>>>>> +           state->closid == state->next_closid)
>>>>> +               return;
>>>>> +
>>>>> +       state->rmid = state->next_rmid;
>>>>> +       state->closid = state->next_closid;
>>>>> +       wrmsr(MSR_IA32_PQR_ASSOC, state->rmid, state->closid);
>>>>> +}
>>>>> --
>>>>> 2.8.0.rc3.226.g39d4020
>>>>>
>>>>>
>>>>
>>>
>>
>

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