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Date: Wed, 25 Sep 2013 15:36:29 -0700
From: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To: Jiri Olsa <jolsa@...hat.com>
Cc: linux-kernel@...r.kernel.org,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 05/21] perf: Add event toggle sys_perf_event_open
interface
Jiri Olsa [jolsa@...hat.com] wrote:
| Adding perf interface that allows to create 'toggle' events,
| which can enable or disable another event. Whenever the toggle
| event is triggered (has overflow), it toggles another event
| state and either starts or stops it.
Nice idea. It would be very useful.
Will try out the patchset, but couple of small comments below.
|
| The goal is to be able to create toggling tracepoint events
| to enable and disable HW counters, but the interface is generic
| enough to be used for any kind of event.
|
| The interface to create a toggle event is similar as the one
| for defining event group. Use perf syscall with:
|
| flags - PERF_FLAG_TOGGLE_ON or PERF_FLAG_TOGGLE_OFF
| group_fd - event (or group) fd to be toggled
|
| Created event will toggle ON(start) or OFF(stop) the event
| specified via group_fd.
|
| Obviously this way it's not possible for toggle event to
| be part of group other than group leader. This will be
| possible via ioctl coming in next patch.
|
| Original-patch-by: Frederic Weisbecker <fweisbec@...il.com>
| Signed-off-by: Jiri Olsa <jolsa@...hat.com>
| Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
| Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
| Cc: Frederic Weisbecker <fweisbec@...il.com>
| Cc: Ingo Molnar <mingo@...e.hu>
| Cc: Paul Mackerras <paulus@...ba.org>
| Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
| Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
| ---
| include/linux/perf_event.h | 9 +++
| include/uapi/linux/perf_event.h | 3 +
| kernel/events/core.c | 158 ++++++++++++++++++++++++++++++++++++++--
| 3 files changed, 164 insertions(+), 6 deletions(-)
|
| diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
| index 866e85c..6ede25c 100644
| --- a/include/linux/perf_event.h
| +++ b/include/linux/perf_event.h
| @@ -289,6 +289,12 @@ struct swevent_hlist {
| struct perf_cgroup;
| struct ring_buffer;
|
| +enum perf_event_toggle_flag {
| + PERF_TOGGLE_NONE = 0,
| + PERF_TOGGLE_ON = 1,
| + PERF_TOGGLE_OFF = 2,
| +};
Can we call this 'perf_event_toggle_state' ? it can be confusing with
PERF_FLAG_TOGGLE* macros below which apply to a different field.
| +
| /**
| * struct perf_event - performance event kernel representation:
| */
| @@ -414,6 +420,9 @@ struct perf_event {
| int cgrp_defer_enabled;
| #endif
|
| + struct perf_event *toggled_event;
| + enum perf_event_toggle_flag toggle_flag;
s/toggle_flag/toggle_state/ ?
| + int paused;
There is an 'event->state' field with OFF, INACTIVE, ACTIVE states.
Can we add a 'PAUSED' state to that instead ?
| #endif /* CONFIG_PERF_EVENTS */
| };
|
| diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
| index ca1d90b..ecb0474 100644
| --- a/include/uapi/linux/perf_event.h
| +++ b/include/uapi/linux/perf_event.h
| @@ -694,6 +694,9 @@ enum perf_callchain_context {
| #define PERF_FLAG_FD_NO_GROUP (1U << 0)
| #define PERF_FLAG_FD_OUTPUT (1U << 1)
| #define PERF_FLAG_PID_CGROUP (1U << 2) /* pid=cgroup id, per-cpu mode only */
| +#define PERF_FLAG_TOGGLE_ON (1U << 3)
| +#define PERF_FLAG_TOGGLE_OFF (1U << 4)
| +
|
| union perf_mem_data_src {
| __u64 val;
| diff --git a/kernel/events/core.c b/kernel/events/core.c
| index e8674e4..40c792d 100644
| --- a/kernel/events/core.c
| +++ b/kernel/events/core.c
| @@ -44,6 +44,8 @@
|
| #include <asm/irq_regs.h>
|
| +#define PERF_FLAG_TOGGLE (PERF_FLAG_TOGGLE_ON | PERF_FLAG_TOGGLE_OFF)
| +
| struct remote_function_call {
| struct task_struct *p;
| int (*func)(void *info);
| @@ -119,7 +121,9 @@ static int cpu_function_call(int cpu, int (*func) (void *info), void *info)
|
| #define PERF_FLAG_ALL (PERF_FLAG_FD_NO_GROUP |\
| PERF_FLAG_FD_OUTPUT |\
| - PERF_FLAG_PID_CGROUP)
| + PERF_FLAG_PID_CGROUP |\
| + PERF_FLAG_TOGGLE_ON |\
| + PERF_FLAG_TOGGLE_OFF)
|
| /*
| * branch priv levels that need permission checks
| @@ -1358,6 +1362,25 @@ out:
| perf_event__header_size(tmp);
| }
|
| +static void put_event(struct perf_event *event);
| +
| +static void __perf_event_toggle_detach(struct perf_event *event)
| +{
| + struct perf_event *toggled_event = event->toggled_event;
| +
| + event->toggle_flag = PERF_TOGGLE_NONE;
| + event->overflow_handler = NULL;
| + event->toggled_event = NULL;
| +
| + put_event(toggled_event);
| +}
| +
| +static void perf_event_toggle_detach(struct perf_event *event)
| +{
| + if (event->toggle_flag > PERF_TOGGLE_NONE)
| + __perf_event_toggle_detach(event);
| +}
| +
| static inline int
| event_filter_match(struct perf_event *event)
| {
| @@ -1646,6 +1669,7 @@ event_sched_in(struct perf_event *event,
| struct perf_event_context *ctx)
| {
| u64 tstamp = perf_event_time(event);
| + int add_flags = PERF_EF_START;
|
| if (event->state <= PERF_EVENT_STATE_OFF)
| return 0;
| @@ -1665,7 +1689,10 @@ event_sched_in(struct perf_event *event,
| */
| smp_wmb();
|
| - if (event->pmu->add(event, PERF_EF_START)) {
| + if (event->paused)
| + add_flags = 0;
| +
| + if (event->pmu->add(event, add_flags)) {
| event->state = PERF_EVENT_STATE_INACTIVE;
| event->oncpu = -1;
| return -EAGAIN;
| @@ -2723,7 +2750,7 @@ static void perf_adjust_freq_unthr_context(struct perf_event_context *ctx,
| event->pmu->start(event, 0);
| }
|
| - if (!event->attr.freq || !event->attr.sample_freq)
| + if (!event->attr.freq || !event->attr.sample_freq || event->paused)
| continue;
|
| /*
| @@ -3240,7 +3267,7 @@ int perf_event_release_kernel(struct perf_event *event)
| raw_spin_unlock_irq(&ctx->lock);
| perf_remove_from_context(event);
| mutex_unlock(&ctx->mutex);
| -
| + perf_event_toggle_detach(event);
| free_event(event);
|
| return 0;
| @@ -5231,6 +5258,72 @@ static void perf_log_throttle(struct perf_event *event, int enable)
| }
|
| /*
| + * TODO:
| + * - fix race when interrupting event_sched_in/event_sched_out
| + * - fix race against other toggler
| + * - fix race against other callers of ->stop/start (adjust period/freq)
| + */
| +static void perf_event_toggle(struct perf_event *event,
| + enum perf_event_toggle_flag flag)
| +{
| + unsigned long flags;
| + bool active;
| +
| + /*
| + * Prevent from races against event->add/del through
| + * preempt_schedule_irq() or enable/disable IPIs
| + */
| + local_irq_save(flags);
| +
| + /* Could be out of HW counter. */
| + active = event->state == PERF_EVENT_STATE_ACTIVE;
| +
| + switch (flag) {
| + case PERF_TOGGLE_ON:
| + if (!event->paused)
| + break;
| + if (active)
| + event->pmu->start(event, PERF_EF_RELOAD);
| + event->paused = false;
| + break;
| + case PERF_TOGGLE_OFF:
| + if (event->paused)
| + break;
| + if (active)
| + event->pmu->stop(event, PERF_EF_UPDATE);
| + event->paused = true;
| + break;
| + case PERF_TOGGLE_NONE:
| + break;
| + }
| +
| + local_irq_restore(flags);
| +}
| +
| +static void
| +perf_event_toggle_overflow(struct perf_event *event,
| + struct perf_sample_data *data,
| + struct pt_regs *regs)
| +{
| + struct perf_event *toggled_event;
| +
| + if (!event->toggle_flag)
| + return;
| +
| + toggled_event = event->toggled_event;
| +
| + if (WARN_ON_ONCE(!toggled_event))
| + return;
| +
| + perf_pmu_disable(toggled_event->pmu);
| +
| + perf_event_toggle(toggled_event, event->toggle_flag);
| + perf_event_output(event, data, regs);
| +
| + perf_pmu_enable(toggled_event->pmu);
| +}
| +
| +/*
| * Generic event overflow handling, sampling.
| */
|
| @@ -6887,6 +6980,43 @@ out:
| return ret;
| }
|
| +static enum perf_event_toggle_flag get_toggle_flag(unsigned long flags)
| +{
| + if ((flags & PERF_FLAG_TOGGLE) == PERF_FLAG_TOGGLE_ON)
| + return PERF_TOGGLE_ON;
| + else if ((flags & PERF_FLAG_TOGGLE) == PERF_FLAG_TOGGLE_OFF)
| + return PERF_TOGGLE_OFF;
| +
| + return PERF_TOGGLE_NONE;
| +}
| +
| +static int
| +perf_event_set_toggle(struct perf_event *event,
| + struct perf_event *toggled_event,
| + struct perf_event_context *ctx,
| + unsigned long flags)
| +{
| + if (WARN_ON_ONCE(!(flags & PERF_FLAG_TOGGLE)))
| + return -EINVAL;
| +
| + /* It's either ON or OFF. */
| + if ((flags & PERF_FLAG_TOGGLE) == PERF_FLAG_TOGGLE)
| + return -EINVAL;
| +
| + /* Allow only same cpu, */
| + if (toggled_event->cpu != event->cpu)
| + return -EINVAL;
| +
| + /* or same task. */
nit: s/or/and/
| + if (toggled_event->ctx->task != ctx->task)
| + return -EINVAL;
| +
| + event->overflow_handler = perf_event_toggle_overflow;
| + event->toggle_flag = get_toggle_flag(flags);
| + event->toggled_event = toggled_event;
| + return 0;
| +}
| +
| /**
| * sys_perf_event_open - open a performance event, associate it to a task/cpu
| *
| @@ -6900,6 +7030,7 @@ SYSCALL_DEFINE5(perf_event_open,
| pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)
| {
| struct perf_event *group_leader = NULL, *output_event = NULL;
| + struct perf_event *toggled_event = NULL;
| struct perf_event *event, *sibling;
| struct perf_event_attr attr;
| struct perf_event_context *ctx;
| @@ -6949,7 +7080,9 @@ SYSCALL_DEFINE5(perf_event_open,
| group_leader = group.file->private_data;
| if (flags & PERF_FLAG_FD_OUTPUT)
| output_event = group_leader;
| - if (flags & PERF_FLAG_FD_NO_GROUP)
| + if (flags & PERF_FLAG_TOGGLE)
| + toggled_event = group_leader;
| + if (flags & (PERF_FLAG_FD_NO_GROUP|PERF_FLAG_TOGGLE))
| group_leader = NULL;
| }
|
| @@ -7060,10 +7193,20 @@ SYSCALL_DEFINE5(perf_event_open,
| goto err_context;
| }
|
| + if (toggled_event) {
| + err = -EINVAL;
| + if (!atomic_long_inc_not_zero(&toggled_event->refcount))
| + goto err_context;
| +
| + err = perf_event_set_toggle(event, toggled_event, ctx, flags);
| + if (err)
| + goto err_toggle;
| + }
| +
| event_file = anon_inode_getfile("[perf_event]", &perf_fops, event, O_RDWR);
| if (IS_ERR(event_file)) {
| err = PTR_ERR(event_file);
| - goto err_context;
| + goto err_toggle;
| }
|
| if (move_group) {
| @@ -7131,6 +7274,9 @@ SYSCALL_DEFINE5(perf_event_open,
| fd_install(event_fd, event_file);
| return event_fd;
|
| +err_toggle:
| + if (toggled_event)
| + put_event(toggled_event);
| err_context:
| perf_unpin_context(ctx);
| put_ctx(ctx);
| --
| 1.7.11.7
|
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