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Message-ID: <aCzBDaHdELjiKHfc@google.com>
Date: Tue, 20 May 2025 10:51:09 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: Mingwei Zhang <mizhang@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>, Liang@...gle.com,
"H. Peter Anvin" <hpa@...or.com>, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
linux-kselftest@...r.kernel.org, Yongwei Ma <yongwei.ma@...el.com>,
Xiong Zhang <xiong.y.zhang@...ux.intel.com>,
Dapeng Mi <dapeng1.mi@...ux.intel.com>,
Jim Mattson <jmattson@...gle.com>,
Sandipan Das <sandipan.das@....com>,
Zide Chen <zide.chen@...el.com>,
Eranian Stephane <eranian@...gle.com>,
Shukla Manali <Manali.Shukla@....com>,
Nikunj Dadhania <nikunj.dadhania@....com>
Subject: Re: [PATCH v4 04/38] perf: Add a EVENT_GUEST flag
On Tue, May 20, 2025 at 12:09:02PM -0400, Liang, Kan wrote:
>
>
> On 2025-05-19 2:58 a.m., Namhyung Kim wrote:
> > Hello,
> >
> > On Mon, Mar 24, 2025 at 05:30:44PM +0000, Mingwei Zhang wrote:
> >> From: Kan Liang <kan.liang@...ux.intel.com>
> >>
> >> Current perf doesn't explicitly schedule out all exclude_guest events
> >> while the guest is running. There is no problem with the current
> >> emulated vPMU. Because perf owns all the PMU counters. It can mask the
> >> counter which is assigned to an exclude_guest event when a guest is
> >> running (Intel way), or set the corresponding HOSTONLY bit in evsentsel
> >> (AMD way). The counter doesn't count when a guest is running.
> >>
> >> However, either way doesn't work with the introduced passthrough vPMU.
> >> A guest owns all the PMU counters when it's running. The host should not
> >> mask any counters. The counter may be used by the guest. The evsentsel
> >> may be overwritten.
> >>
> >> Perf should explicitly schedule out all exclude_guest events to release
> >> the PMU resources when entering a guest, and resume the counting when
> >> exiting the guest.
> >>
> >> It's possible that an exclude_guest event is created when a guest is
> >> running. The new event should not be scheduled in as well.
> >>
> >> The ctx time is shared among different PMUs. The time cannot be stopped
> >> when a guest is running. It is required to calculate the time for events
> >> from other PMUs, e.g., uncore events. Add timeguest to track the guest
> >> run time. For an exclude_guest event, the elapsed time equals
> >> the ctx time - guest time.
> >> Cgroup has dedicated times. Use the same method to deduct the guest time
> >> from the cgroup time as well.
> >>
> >> Co-developed-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> >> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> >> Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
> >> Signed-off-by: Mingwei Zhang <mizhang@...gle.com>
> >> ---
> >> include/linux/perf_event.h | 6 ++
> >> kernel/events/core.c | 209 +++++++++++++++++++++++++++++--------
> >> 2 files changed, 169 insertions(+), 46 deletions(-)
> >>
> >> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> >> index a2fd1bdc955c..7bda1e20be12 100644
> >> --- a/include/linux/perf_event.h
> >> +++ b/include/linux/perf_event.h
> >> @@ -999,6 +999,11 @@ struct perf_event_context {
> >> */
> >> struct perf_time_ctx time;
> >>
> >> + /*
> >> + * Context clock, runs when in the guest mode.
> >> + */
> >> + struct perf_time_ctx timeguest;
> >
> > Why not make it an array as you use it later?
>
> Do you mean
> struct perf_time_ctx times[2]?
Yep.
>
> I don't see a big benefit of using times[T_GUEST] VS.timeguest.
No big benefits. But I just think it's natural to make it an array if
you want to access them as if it's an array. :)
>
> >
> >> +
> >> /*
> >> * These fields let us detect when two contexts have both
> >> * been cloned (inherited) from a common ancestor.
> >> @@ -1089,6 +1094,7 @@ struct bpf_perf_event_data_kern {
> >> */
> >> struct perf_cgroup_info {
> >> struct perf_time_ctx time;
> >> + struct perf_time_ctx timeguest;
> >> int active;
> >> };
> >>
> >> diff --git a/kernel/events/core.c b/kernel/events/core.c
> >> index e38c8b5e8086..7a2115b2c5c1 100644
> >> --- a/kernel/events/core.c
> >> +++ b/kernel/events/core.c
> >> @@ -163,7 +163,8 @@ enum event_type_t {
> >> /* see ctx_resched() for details */
> >> EVENT_CPU = 0x10,
> >> EVENT_CGROUP = 0x20,
> >> - EVENT_FLAGS = EVENT_CGROUP,
> >> + EVENT_GUEST = 0x40,
> >
> > It's not clear to me if this flag is for events to include guests or
> > exclude them. Can you please add a comment?
> >
>
> /*
> * There are guest events. The for_each_epc() iteration can
> * skip those PMUs which doesn't support guest events via the
> * MEDIATED_VPMU. It is also used to indicate the start/end of
> * guest events to calculate the guest running time.
> */
Thanks for the explanation. So it's for events with !exclude_guest on
host and to do some operation only for host-only events on mediated
vPMUs.
Thanks,
Namhyung
> >
> >> + EVENT_FLAGS = EVENT_CGROUP | EVENT_GUEST,
> >> /* compound helpers */
> >> EVENT_ALL = EVENT_FLEXIBLE | EVENT_PINNED,
> >> EVENT_TIME_FROZEN = EVENT_TIME | EVENT_FROZEN,
> >> @@ -435,6 +436,7 @@ static atomic_t nr_include_guest_events __read_mostly;
> >>
> >> static atomic_t nr_mediated_pmu_vms;
> >> static DEFINE_MUTEX(perf_mediated_pmu_mutex);
> >> +static DEFINE_PER_CPU(bool, perf_in_guest);
> >>
> >> /* !exclude_guest event of PMU with PERF_PMU_CAP_MEDIATED_VPMU */
> >> static inline bool is_include_guest_event(struct perf_event *event)
> >> @@ -738,6 +740,9 @@ static bool perf_skip_pmu_ctx(struct perf_event_pmu_context *pmu_ctx,
> >> {
> >> if ((event_type & EVENT_CGROUP) && !pmu_ctx->nr_cgroups)
> >> return true;
> >> + if ((event_type & EVENT_GUEST) &&
> >> + !(pmu_ctx->pmu->capabilities & PERF_PMU_CAP_MEDIATED_VPMU))
> >> + return true;
> >> return false;
> >> }
> >>
> >> @@ -788,6 +793,39 @@ static inline void update_perf_time_ctx(struct perf_time_ctx *time, u64 now, boo
> >> WRITE_ONCE(time->offset, time->time - time->stamp);
> >> }
> >>
> >> +static_assert(offsetof(struct perf_event_context, timeguest) -
> >> + offsetof(struct perf_event_context, time) ==
> >> + sizeof(struct perf_time_ctx));
> >> +
> >> +#define T_TOTAL 0
> >> +#define T_GUEST 1
> >> +
> >> +static inline u64 __perf_event_time_ctx(struct perf_event *event,
> >> + struct perf_time_ctx *times)
> >> +{
> >> + u64 time = times[T_TOTAL].time;
> >> +
> >> + if (event->attr.exclude_guest)
> >> + time -= times[T_GUEST].time;
> >> +
> >> + return time;
> >> +}
> >> +
> >> +static inline u64 __perf_event_time_ctx_now(struct perf_event *event,
> >> + struct perf_time_ctx *times,
> >> + u64 now)
> >> +{
> >> + if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest)) {
> >> + /*
> >> + * (now + times[total].offset) - (now + times[guest].offset) :=
> >> + * times[total].offset - times[guest].offset
> >> + */
> >> + return READ_ONCE(times[T_TOTAL].offset) - READ_ONCE(times[T_GUEST].offset);
> >> + }
> >> +
> >> + return now + READ_ONCE(times[T_TOTAL].offset);
> >> +}
> >> +
> >> #ifdef CONFIG_CGROUP_PERF
> >>
> >> static inline bool
> >> @@ -824,12 +862,16 @@ static inline int is_cgroup_event(struct perf_event *event)
> >> return event->cgrp != NULL;
> >> }
> >>
> >> +static_assert(offsetof(struct perf_cgroup_info, timeguest) -
> >> + offsetof(struct perf_cgroup_info, time) ==
> >> + sizeof(struct perf_time_ctx));
> >> +
> >> static inline u64 perf_cgroup_event_time(struct perf_event *event)
> >> {
> >> struct perf_cgroup_info *t;
> >>
> >> t = per_cpu_ptr(event->cgrp->info, event->cpu);
> >> - return t->time.time;
> >> + return __perf_event_time_ctx(event, &t->time);
> >> }
> >>
> >> static inline u64 perf_cgroup_event_time_now(struct perf_event *event, u64 now)
> >> @@ -838,9 +880,21 @@ static inline u64 perf_cgroup_event_time_now(struct perf_event *event, u64 now)
> >>
> >> t = per_cpu_ptr(event->cgrp->info, event->cpu);
> >> if (!__load_acquire(&t->active))
> >> - return t->time.time;
> >> - now += READ_ONCE(t->time.offset);
> >> - return now;
> >> + return __perf_event_time_ctx(event, &t->time);
> >> +
> >> + return __perf_event_time_ctx_now(event, &t->time, now);
> >> +}
> >> +
> >> +static inline void __update_cgrp_guest_time(struct perf_cgroup_info *info, u64 now, bool adv)
> >> +{
> >> + update_perf_time_ctx(&info->timeguest, now, adv);
> >> +}
> >> +
> >> +static inline void update_cgrp_time(struct perf_cgroup_info *info, u64 now)
> >> +{
> >> + update_perf_time_ctx(&info->time, now, true);
> >> + if (__this_cpu_read(perf_in_guest))
> >> + __update_cgrp_guest_time(info, now, true);
> >> }
> >>
> >> static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx, bool final)
> >> @@ -856,7 +910,7 @@ static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx,
> >> cgrp = container_of(css, struct perf_cgroup, css);
> >> info = this_cpu_ptr(cgrp->info);
> >>
> >> - update_perf_time_ctx(&info->time, now, true);
> >> + update_cgrp_time(info, now);
> >> if (final)
> >> __store_release(&info->active, 0);
> >> }
> >> @@ -879,11 +933,11 @@ static inline void update_cgrp_time_from_event(struct perf_event *event)
> >> * Do not update time when cgroup is not active
> >> */
> >> if (info->active)
> >> - update_perf_time_ctx(&info->time, perf_clock(), true);
> >> + update_cgrp_time(info, perf_clock());
> >> }
> >>
> >> static inline void
> >> -perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx)
> >> +perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx, bool guest)
> >> {
> >> struct perf_event_context *ctx = &cpuctx->ctx;
> >> struct perf_cgroup *cgrp = cpuctx->cgrp;
> >> @@ -903,8 +957,12 @@ perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx)
> >> for (css = &cgrp->css; css; css = css->parent) {
> >> cgrp = container_of(css, struct perf_cgroup, css);
> >> info = this_cpu_ptr(cgrp->info);
> >> - update_perf_time_ctx(&info->time, ctx->time.stamp, false);
> >> - __store_release(&info->active, 1);
> >> + if (guest) {
> >> + __update_cgrp_guest_time(info, ctx->time.stamp, false);
> >> + } else {
> >> + update_perf_time_ctx(&info->time, ctx->time.stamp, false);
> >> + __store_release(&info->active, 1);
> >> + }
> >> }
> >> }
> >>
> >> @@ -1104,7 +1162,7 @@ static inline int perf_cgroup_connect(pid_t pid, struct perf_event *event,
> >> }
> >>
> >> static inline void
> >> -perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx)
> >> +perf_cgroup_set_timestamp(struct perf_cpu_context *cpuctx, bool guest)
> >> {
> >> }
> >>
> >> @@ -1514,16 +1572,24 @@ static void perf_unpin_context(struct perf_event_context *ctx)
> >> */
> >> static void __update_context_time(struct perf_event_context *ctx, bool adv)
> >> {
> >> - u64 now = perf_clock();
> >> + lockdep_assert_held(&ctx->lock);
> >> +
> >> + update_perf_time_ctx(&ctx->time, perf_clock(), adv);
> >> +}
> >>
> >> +static void __update_context_guest_time(struct perf_event_context *ctx, bool adv)
> >> +{
> >> lockdep_assert_held(&ctx->lock);
> >>
> >> - update_perf_time_ctx(&ctx->time, now, adv);
> >> + /* must be called after __update_context_time(); */
> >> + update_perf_time_ctx(&ctx->timeguest, ctx->time.stamp, adv);
> >> }
> >>
> >> static void update_context_time(struct perf_event_context *ctx)
> >> {
> >> __update_context_time(ctx, true);
> >> + if (__this_cpu_read(perf_in_guest))
> >> + __update_context_guest_time(ctx, true);
> >> }
> >>
> >> static u64 perf_event_time(struct perf_event *event)
> >> @@ -1536,7 +1602,7 @@ static u64 perf_event_time(struct perf_event *event)
> >> if (is_cgroup_event(event))
> >> return perf_cgroup_event_time(event);
> >>
> >> - return ctx->time.time;
> >> + return __perf_event_time_ctx(event, &ctx->time);
> >> }
> >>
> >> static u64 perf_event_time_now(struct perf_event *event, u64 now)
> >> @@ -1550,10 +1616,9 @@ static u64 perf_event_time_now(struct perf_event *event, u64 now)
> >> return perf_cgroup_event_time_now(event, now);
> >>
> >> if (!(__load_acquire(&ctx->is_active) & EVENT_TIME))
> >> - return ctx->time.time;
> >> + return __perf_event_time_ctx(event, &ctx->time);
> >>
> >> - now += READ_ONCE(ctx->time.offset);
> >> - return now;
> >> + return __perf_event_time_ctx_now(event, &ctx->time, now);
> >> }
> >>
> >> static enum event_type_t get_event_type(struct perf_event *event)
> >> @@ -2384,20 +2449,23 @@ group_sched_out(struct perf_event *group_event, struct perf_event_context *ctx)
> >> }
> >>
> >> static inline void
> >> -__ctx_time_update(struct perf_cpu_context *cpuctx, struct perf_event_context *ctx, bool final)
> >> +__ctx_time_update(struct perf_cpu_context *cpuctx, struct perf_event_context *ctx,
> >> + bool final, enum event_type_t event_type)
> >> {
> >> if (ctx->is_active & EVENT_TIME) {
> >> if (ctx->is_active & EVENT_FROZEN)
> >> return;
> >> +
> >> update_context_time(ctx);
> >> - update_cgrp_time_from_cpuctx(cpuctx, final);
> >> + /* vPMU should not stop time */
> >> + update_cgrp_time_from_cpuctx(cpuctx, !(event_type & EVENT_GUEST) && final);
> >> }
> >> }
> >>
> >> static inline void
> >> ctx_time_update(struct perf_cpu_context *cpuctx, struct perf_event_context *ctx)
> >> {
> >> - __ctx_time_update(cpuctx, ctx, false);
> >> + __ctx_time_update(cpuctx, ctx, false, 0);
> >> }
> >>
> >> /*
> >> @@ -3405,7 +3473,7 @@ ctx_sched_out(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t
> >> *
> >> * would only update time for the pinned events.
> >> */
> >> - __ctx_time_update(cpuctx, ctx, ctx == &cpuctx->ctx);
> >> + __ctx_time_update(cpuctx, ctx, ctx == &cpuctx->ctx, event_type);
> >>
> >> /*
> >> * CPU-release for the below ->is_active store,
> >> @@ -3431,7 +3499,18 @@ ctx_sched_out(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t
> >> cpuctx->task_ctx = NULL;
> >> }
> >>
> >> - is_active ^= ctx->is_active; /* changed bits */
> >> + if (event_type & EVENT_GUEST) {
> >> + /*
> >> + * Schedule out all exclude_guest events of PMU
> >> + * with PERF_PMU_CAP_MEDIATED_VPMU.
> >> + */
> >> + is_active = EVENT_ALL;
> >> + __update_context_guest_time(ctx, false);
> >> + perf_cgroup_set_timestamp(cpuctx, true);
> >> + barrier();
> >> + } else {
> >> + is_active ^= ctx->is_active; /* changed bits */
> >> + }
> >>
> >> for_each_epc(pmu_ctx, ctx, pmu, event_type)
> >> __pmu_ctx_sched_out(pmu_ctx, is_active);
> >> @@ -3926,10 +4005,15 @@ static inline void group_update_userpage(struct perf_event *group_event)
> >> event_update_userpage(event);
> >> }
> >>
> >> +struct merge_sched_data {
> >> + int can_add_hw;
> >> + enum event_type_t event_type;
> >> +};
> >> +
> >> static int merge_sched_in(struct perf_event *event, void *data)
> >> {
> >> struct perf_event_context *ctx = event->ctx;
> >> - int *can_add_hw = data;
> >> + struct merge_sched_data *msd = data;
> >>
> >> if (event->state <= PERF_EVENT_STATE_OFF)
> >> return 0;
> >> @@ -3937,13 +4021,22 @@ static int merge_sched_in(struct perf_event *event, void *data)
> >> if (!event_filter_match(event))
> >> return 0;
> >>
> >> - if (group_can_go_on(event, *can_add_hw)) {
> >> + /*
> >> + * Don't schedule in any host events from PMU with
> >> + * PERF_PMU_CAP_MEDIATED_VPMU, while a guest is running.
> >> + */
> >> + if (__this_cpu_read(perf_in_guest) &&
> >> + event->pmu_ctx->pmu->capabilities & PERF_PMU_CAP_MEDIATED_VPMU &&
> >> + !(msd->event_type & EVENT_GUEST))
> >> + return 0;
> >> +
> >> + if (group_can_go_on(event, msd->can_add_hw)) {
> >> if (!group_sched_in(event, ctx))
> >> list_add_tail(&event->active_list, get_event_list(event));
> >> }
> >>
> >> if (event->state == PERF_EVENT_STATE_INACTIVE) {
> >> - *can_add_hw = 0;
> >> + msd->can_add_hw = 0;
> >> if (event->attr.pinned) {
> >> perf_cgroup_event_disable(event, ctx);
> >> perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
> >> @@ -3962,11 +4055,15 @@ static int merge_sched_in(struct perf_event *event, void *data)
> >>
> >> static void pmu_groups_sched_in(struct perf_event_context *ctx,
> >> struct perf_event_groups *groups,
> >> - struct pmu *pmu)
> >> + struct pmu *pmu,
> >> + enum event_type_t event_type)
> >> {
> >> - int can_add_hw = 1;
> >> + struct merge_sched_data msd = {
> >> + .can_add_hw = 1,
> >> + .event_type = event_type,
> >> + };
> >> visit_groups_merge(ctx, groups, smp_processor_id(), pmu,
> >> - merge_sched_in, &can_add_hw);
> >> + merge_sched_in, &msd);
> >> }
> >>
> >> static void __pmu_ctx_sched_in(struct perf_event_pmu_context *pmu_ctx,
> >> @@ -3975,9 +4072,9 @@ static void __pmu_ctx_sched_in(struct perf_event_pmu_context *pmu_ctx,
> >> struct perf_event_context *ctx = pmu_ctx->ctx;
> >>
> >> if (event_type & EVENT_PINNED)
> >> - pmu_groups_sched_in(ctx, &ctx->pinned_groups, pmu_ctx->pmu);
> >> + pmu_groups_sched_in(ctx, &ctx->pinned_groups, pmu_ctx->pmu, event_type);
> >> if (event_type & EVENT_FLEXIBLE)
> >> - pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu_ctx->pmu);
> >> + pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu_ctx->pmu, event_type);
> >> }
> >>
> >> static void
> >> @@ -3994,9 +4091,11 @@ ctx_sched_in(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t
> >> return;
> >>
> >> if (!(is_active & EVENT_TIME)) {
> >> + /* EVENT_TIME should be active while the guest runs */
> >> + WARN_ON_ONCE(event_type & EVENT_GUEST);
> >> /* start ctx time */
> >> __update_context_time(ctx, false);
> >> - perf_cgroup_set_timestamp(cpuctx);
> >> + perf_cgroup_set_timestamp(cpuctx, false);
> >> /*
> >> * CPU-release for the below ->is_active store,
> >> * see __load_acquire() in perf_event_time_now()
> >> @@ -4012,7 +4111,23 @@ ctx_sched_in(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t
> >> WARN_ON_ONCE(cpuctx->task_ctx != ctx);
> >> }
> >>
> >> - is_active ^= ctx->is_active; /* changed bits */
> >> + if (event_type & EVENT_GUEST) {
> >> + /*
> >> + * Schedule in the required exclude_guest events of PMU
> >> + * with PERF_PMU_CAP_MEDIATED_VPMU.
> >> + */
> >> + is_active = event_type & EVENT_ALL;
> >> +
> >> + /*
> >> + * Update ctx time to set the new start time for
> >> + * the exclude_guest events.
> >> + */
> >> + update_context_time(ctx);
> >> + update_cgrp_time_from_cpuctx(cpuctx, false);
> >> + barrier();
> >> + } else {
> >> + is_active ^= ctx->is_active; /* changed bits */
> >> + }
> >>
> >> /*
> >> * First go through the list and put on any pinned groups
> >> @@ -4020,13 +4135,13 @@ ctx_sched_in(struct perf_event_context *ctx, struct pmu *pmu, enum event_type_t
> >> */
> >> if (is_active & EVENT_PINNED) {
> >> for_each_epc(pmu_ctx, ctx, pmu, event_type)
> >> - __pmu_ctx_sched_in(pmu_ctx, EVENT_PINNED);
> >> + __pmu_ctx_sched_in(pmu_ctx, EVENT_PINNED | (event_type & EVENT_GUEST));
> >> }
> >>
> >> /* Then walk through the lower prio flexible groups */
> >> if (is_active & EVENT_FLEXIBLE) {
> >> for_each_epc(pmu_ctx, ctx, pmu, event_type)
> >> - __pmu_ctx_sched_in(pmu_ctx, EVENT_FLEXIBLE);
> >> + __pmu_ctx_sched_in(pmu_ctx, EVENT_FLEXIBLE | (event_type & EVENT_GUEST));
> >> }
> >> }
> >>
> >> @@ -6285,23 +6400,25 @@ void perf_event_update_userpage(struct perf_event *event)
> >> if (!rb)
> >> goto unlock;
> >>
> >> - /*
> >> - * compute total_time_enabled, total_time_running
> >> - * based on snapshot values taken when the event
> >> - * was last scheduled in.
> >> - *
> >> - * we cannot simply called update_context_time()
> >> - * because of locking issue as we can be called in
> >> - * NMI context
> >> - */
> >> - calc_timer_values(event, &now, &enabled, &running);
> >> -
> >> - userpg = rb->user_page;
> >> /*
> >> * Disable preemption to guarantee consistent time stamps are stored to
> >> * the user page.
> >> */
> >> preempt_disable();
> >> +
> >> + /*
> >> + * compute total_time_enabled, total_time_running
> >> + * based on snapshot values taken when the event
> >> + * was last scheduled in.
> >> + *
> >> + * we cannot simply called update_context_time()
> >> + * because of locking issue as we can be called in
> >> + * NMI context
> >> + */
> >> + calc_timer_values(event, &now, &enabled, &running);
> >> +
> >> + userpg = rb->user_page;
> >> +
> >> ++userpg->lock;
> >> barrier();
> >> userpg->index = perf_event_index(event);
> >> --
> >> 2.49.0.395.g12beb8f557-goog
> >>
> >
>
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