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@xxxxxxxxxxxxxxx>
>>
>> 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@xxxxxxxxxxxxx>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
>> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
>> ---
>> 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]?
I don't see a big benefit of using times[T_GUEST] VS.timeguest.
>
>> +
>> /*
>> * 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,
Kan
> 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
>>
>
