Date:	Fri, 29 Apr 2016 14:49:28 -0700
From:	David Carrillo-Cisneros <davidcc@...gle.com>
To:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Cc:	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

When an event is terminated, intel_cqm_event_stop calls
pqr_cache_update_rmid and sets state->next_rmid to the rmid of its
parent in the RMID hierarchy. That would make next call to
__pqr_update to update PQR_ASSOC.

On Fri, Apr 29, 2016 at 2:32 PM Vikas Shivappa
<vikas.shivappa@...ux.intel.com> wrote:
>
>
>
> 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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