Re: [PATCH v2 07/54] perf: Add generic exclude_guest support

Liang, Kan
2024-06-13T18:04:41Z

On 2024-06-13 9:37 a.m., Liang, Kan wrote:
>> ---
>>
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -947,7 +947,9 @@ struct perf_event_context {
>> u64 time;
>> u64 timestamp;
>> u64 timeoffset;
>> - u64 timeguest;
>> + u64 guest_time;
>> + u64 guest_timestamp;
>> + u64 guest_timeoffset;
>>
>> /*
>> * These fields let us detect when two contexts have both
>> @@ -1043,6 +1045,9 @@ struct perf_cgroup_info {
>> u64 time;
>> u64 timestamp;
>> u64 timeoffset;
>> + u64 guest_time;
>> + u64 guest_timestamp;
>> + u64 guest_timeoffset;
>> int active;
>> };
>>
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -638,26 +638,9 @@ __perf_update_times(struct perf_event *e
>>
>> static void perf_event_update_time(struct perf_event *event)
>> {
>> - u64 now;
>> -
>> - /* Never count the time of an active guest into an exclude_guest event. */
>> - if (event->ctx->timeguest &&
>> - event->pmu->capabilities & PERF_PMU_CAP_PASSTHROUGH_VPMU) {
>> - /*
>> - * If a guest is running, use the timestamp while entering the guest.
>> - * If the guest is leaving, reset the event timestamp.
>> - */
>> - if (__this_cpu_read(perf_in_guest))
>> - event->tstamp = event->ctx->timeguest;
>> - else
>> - event->tstamp = event->ctx->time;
>> - return;
>> - }
>> -
>> - now = perf_event_time(event);
>> + u64 now = perf_event_time(event);
>> __perf_update_times(event, now, &event->total_time_enabled,
>> &event->total_time_running);
>> -
>> event->tstamp = now;
>> }
>>
>> @@ -780,19 +763,33 @@ static inline int is_cgroup_event(struct
>> static inline u64 perf_cgroup_event_time(struct perf_event *event)
>> {
>> struct perf_cgroup_info *t;
>> + u64 time;
>>
>> t = per_cpu_ptr(event->cgrp->info, event->cpu);
>> - return t->time;
>> + time = t->time;
>> + if (event->attr.exclude_guest)
>> + time -= t->guest_time;
>> + return time;
>> }
>>
>> static inline u64 perf_cgroup_event_time_now(struct perf_event *event, u64 now)
>> {
>> struct perf_cgroup_info *t;
>> + u64 time, guest_time;
>>
>> t = per_cpu_ptr(event->cgrp->info, event->cpu);
>> - if (!__load_acquire(&t->active))
>> - return t->time;
>> - now += READ_ONCE(t->timeoffset);
>> + if (!__load_acquire(&t->active)) {
>> + time = t->time;
>> + if (event->attr.exclude_guest)
>> + time -= t->guest_time;
>> + return time;
>> + }
>> +
>> + time = now + READ_ONCE(t->timeoffset);
>> + if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest)) {
>> + guest_time = now + READ_ONCE(t->guest_offset);
>> + time -= guest_time;
>> + }
>> return now;
>> }
>>
>> @@ -807,6 +804,17 @@ static inline void __update_cgrp_time(st
>> WRITE_ONCE(info->timeoffset, info->time - info->timestamp);
>> }
>>
>> +static inline void __update_cgrp_guest_time(struct perf_cgroup_info *info, u64 now, bool adv)
>> +{
>> + if (adv)
>> + info->guest_time += now - info->guest_timestamp;
>> + info->guest_timestamp = now;
>> + /*
>> + * see update_context_time()
>> + */
>> + WRITE_ONCE(info->guest_timeoffset, info->guest_time - info->guest_timestamp);
>> +}
>> +
>> static inline void update_cgrp_time_from_cpuctx(struct perf_cpu_context *cpuctx, bool final)
>> {
>> struct perf_cgroup *cgrp = cpuctx->cgrp;
>> @@ -821,6 +829,8 @@ static inline void update_cgrp_time_from
>> info = this_cpu_ptr(cgrp->info);
>>
>> __update_cgrp_time(info, now, true);
>> + if (__this_cpu_read(perf_in_guest))
>> + __update_cgrp_guest_time(info, now, true);
>> if (final)
>> __store_release(&info->active, 0);
>> }
>> @@ -1501,14 +1511,39 @@ static void __update_context_time(struct
>> WRITE_ONCE(ctx->timeoffset, ctx->time - ctx->timestamp);
>> }
>>
>> +static void __update_context_guest_time(struct perf_event_context *ctx, bool adv)
>> +{
>> + u64 now = ctx->timestamp; /* must be called after __update_context_time(); */
>> +
>> + lockdep_assert_held(&ctx->lock);
>> +
>> + if (adv)
>> + ctx->guest_time += now - ctx->guest_timestamp;
>> + ctx->guest_timestamp = now;
>> +
>> + /*
>> + * The above: time' = time + (now - timestamp), can be re-arranged
>> + * into: time` = now + (time - timestamp), which gives a single value
>> + * offset to compute future time without locks on.
>> + *
>> + * See perf_event_time_now(), which can be used from NMI context where
>> + * it's (obviously) not possible to acquire ctx->lock in order to read
>> + * both the above values in a consistent manner.
>> + */
>> + WRITE_ONCE(ctx->guest_timeoffset, ctx->guest_time - ctx->guest_timestamp);
>> +}
>> +
>> 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)
>> {
>> struct perf_event_context *ctx = event->ctx;
>> + u64 time;
>>
>> if (unlikely(!ctx))
>> return 0;
>> @@ -1516,12 +1551,17 @@ static u64 perf_event_time(struct perf_e
>> if (is_cgroup_event(event))
>> return perf_cgroup_event_time(event);
>>
>> - return ctx->time;
>> + time = ctx->time;
>> + if (event->attr.exclude_guest)
>> + time -= ctx->guest_time;
>> +
>> + return time;
>> }
>>
>> static u64 perf_event_time_now(struct perf_event *event, u64 now)
>> {
>> struct perf_event_context *ctx = event->ctx;
>> + u64 time, guest_time;
>>
>> if (unlikely(!ctx))
>> return 0;
>> @@ -1529,11 +1569,19 @@ static u64 perf_event_time_now(struct pe
>> if (is_cgroup_event(event))
>> return perf_cgroup_event_time_now(event, now);
>>
>> - if (!(__load_acquire(&ctx->is_active) & EVENT_TIME))
>> - return ctx->time;
>> + if (!(__load_acquire(&ctx->is_active) & EVENT_TIME)) {
>> + time = ctx->time;
>> + if (event->attr.exclude_guest)
>> + time -= ctx->guest_time;
>> + return time;
>> + }
>>
>> - now += READ_ONCE(ctx->timeoffset);
>> - return now;
>> + time = now + READ_ONCE(ctx->timeoffset);
>> + if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest)) {
>> + guest_time = now + READ_ONCE(ctx->guest_timeoffset);
>> + time -= guest_time;
>> + }
>> + return time;
>> }
>>
>> static enum event_type_t get_event_type(struct perf_event *event)
>> @@ -3340,9 +3388,14 @@ ctx_sched_out(struct perf_event_context
>> * would only update time for the pinned events.
>> */
>> if (is_active & EVENT_TIME) {
>> + bool stop;
>> +
>> + stop = !((ctx->is_active & event_type) & EVENT_ALL) &&
>> + ctx == &cpuctx->ctx;
>> +
>> /* update (and stop) ctx time */
>> update_context_time(ctx);
>> - update_cgrp_time_from_cpuctx(cpuctx, ctx == &cpuctx->ctx);
>> + update_cgrp_time_from_cpuctx(cpuctx, stop);

For the event_type == EVENT_GUEST, the "stop" should always be the same
as "ctx == &cpuctx->ctx". Because the ctx->is_active never set the
EVENT_GUEST bit.
Why the stop is introduced?

>> /*
>> * CPU-release for the below ->is_active store,
>> * see __load_acquire() in perf_event_time_now()
>> @@ -3366,8 +3419,12 @@ ctx_sched_out(struct perf_event_context
>> * with PERF_PMU_CAP_PASSTHROUGH_VPMU.
>> */
>> is_active = EVENT_ALL;
>> - } else
>> + __update_context_guest_time(ctx, false);
>> + perf_cgroup_set_guest_timestamp(cpuctx);
>> + barrier();
>> + } else {
>> is_active ^= ctx->is_active; /* changed bits */
>> + }
>>
>> list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
>> if (perf_skip_pmu_ctx(pmu_ctx, event_type))
>> @@ -3866,10 +3923,15 @@ static inline void group_update_userpage
>> 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;
>> @@ -3881,18 +3943,18 @@ static int merge_sched_in(struct perf_ev
>> * Don't schedule in any exclude_guest events of PMU with
>> * PERF_PMU_CAP_PASSTHROUGH_VPMU, while a guest is running.
>> */
>> - if (__this_cpu_read(perf_in_guest) &&
>> - event->pmu->capabilities & PERF_PMU_CAP_PASSTHROUGH_VPMU &&
>> - event->attr.exclude_guest)
>> + if (event->attr.exclude_guest && __this_cpu_read(perf_in_guest) &&
>> + (event->pmu->capabilities & PERF_PMU_CAP_PASSTHROUGH_VPMU) &&
>> + !(msd->event_type & EVENT_GUEST))
>> return 0;
>>
>> - if (group_can_go_on(event, *can_add_hw)) {
>> + 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);
>> @@ -3911,11 +3973,15 @@ static int merge_sched_in(struct perf_ev
>>
>> static void pmu_groups_sched_in(struct perf_event_context *ctx,
>> struct perf_event_groups *groups,
>> - struct pmu *pmu)
>> + struct pmu *pmu,
>> + enum even_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 ctx_groups_sched_in(struct perf_event_context *ctx,
>> @@ -3927,14 +3993,14 @@ static void ctx_groups_sched_in(struct p
>> list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
>> if (perf_skip_pmu_ctx(pmu_ctx, event_type))
>> continue;
>> - pmu_groups_sched_in(ctx, groups, pmu_ctx->pmu);
>> + pmu_groups_sched_in(ctx, groups, pmu_ctx->pmu, event_type);
>> }
>> }
>>
>> static void __pmu_ctx_sched_in(struct perf_event_context *ctx,
>> struct pmu *pmu)
>> {
>> - pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu);
>> + pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu, 0);
>> }
>>
>> static void
>> @@ -3949,6 +4015,8 @@ ctx_sched_in(struct perf_event_context *
>> 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);
>> @@ -3979,8 +4047,11 @@ ctx_sched_in(struct perf_event_context *
>> * the exclude_guest events.
>> */
>> update_context_time(ctx);
>> - } else
>> + update_cgrp_time_from_cpuctx(cpuctx, false);

In the above ctx_sched_out(), the cgrp_time is stopped and the cgrp has
been set to inactive.
I think we need a perf_cgroup_set_timestamp(cpuctx) here to restart the
cgrp_time, Right?

Also, I think the cgrp_time is different from the normal ctx->time. When
a guest is running, there must be no cgroup. It's OK to disable the
cgrp_time. If so, I don't think we need to track the guest_time for the
cgrp.

Thanks,
Kan

>> + barrier();
>> + } else {
>> is_active ^= ctx->is_active; /* changed bits */
>> + }
>>
>> /*
>> * First go through the list and put on any pinned groups
>> @@ -5832,25 +5903,20 @@ void perf_guest_enter(void)
>>
>> perf_ctx_lock(cpuctx, cpuctx->task_ctx);
>>
>> - if (WARN_ON_ONCE(__this_cpu_read(perf_in_guest))) {
>> - perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
>> - return;
>> - }
>> + if (WARN_ON_ONCE(__this_cpu_read(perf_in_guest)))
>> + goto unlock;
>>
>> perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
>> ctx_sched_out(&cpuctx->ctx, EVENT_GUEST);
>> - /* Set the guest start time */
>> - cpuctx->ctx.timeguest = cpuctx->ctx.time;
>> perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);
>> if (cpuctx->task_ctx) {
>> perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);
>> task_ctx_sched_out(cpuctx->task_ctx, EVENT_GUEST);
>> - cpuctx->task_ctx->timeguest = cpuctx->task_ctx->time;
>> perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
>> }
>>
>> __this_cpu_write(perf_in_guest, true);
>> -
>> +unlock:
>> perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
>> }
>>
>> @@ -5862,24 +5928,21 @@ void perf_guest_exit(void)
>>
>> perf_ctx_lock(cpuctx, cpuctx->task_ctx);
>>
>> - if (WARN_ON_ONCE(!__this_cpu_read(perf_in_guest))) {
>> - perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
>> - return;
>> - }
>> -
>> - __this_cpu_write(perf_in_guest, false);
>> + if (WARN_ON_ONCE(!__this_cpu_read(perf_in_guest)))
>> + goto unlock;
>>
>> perf_ctx_disable(&cpuctx->ctx, EVENT_GUEST);
>> ctx_sched_in(&cpuctx->ctx, EVENT_GUEST);
>> - cpuctx->ctx.timeguest = 0;
>> perf_ctx_enable(&cpuctx->ctx, EVENT_GUEST);
>> if (cpuctx->task_ctx) {
>> perf_ctx_disable(cpuctx->task_ctx, EVENT_GUEST);
>> ctx_sched_in(cpuctx->task_ctx, EVENT_GUEST);
>> - cpuctx->task_ctx->timeguest = 0;
>> perf_ctx_enable(cpuctx->task_ctx, EVENT_GUEST);
>> }
>>
>> + __this_cpu_write(perf_in_guest, false);
>> +
>> +unlock:
>> perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
>> }
>>