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Date: Wed, 21 Apr 2010 10:32:54 +0200
From: stephane eranian <eranian@...glemail.com>
To: Lin Ming <ming.m.lin@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
"Gary.Mohr@...l.com" <Gary.Mohr@...l.com>,
Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] perf_events: support for uncore a.k.a. nest units
Seems to me that struct pmu is a shared resource across all CPUs.
I don't understand why scheduling on one CPU would have to impact
all the other CPUs, unless I am missing something here.
On Wed, Apr 21, 2010 at 10:08 AM, Lin Ming <ming.m.lin@...el.com> wrote:
> On Tue, 2010-04-20 at 20:03 +0800, Peter Zijlstra wrote:
>> On Tue, 2010-04-20 at 19:55 +0800, Lin Ming wrote:
>>
>> > > One thing not on that list, which should happen first I guess, is to
>> > > remove hw_perf_group_sched_in(). The idea is to add some sort of
>> > > transactional API to the struct pmu, so that we can delay the
>> > > schedulability check until commit time (and roll back when it fails).
>> > >
>> > > Something as simple as:
>> > >
>> > > struct pmu {
>> > > void start_txn(struct pmu *);
>> > > void commit_txn(struct pmu *);
>> > >
>> > > ,,,
>> > > };
>> >
>> > Could you please explain a bit more?
>> >
>> > Does it mean that "start_txn" perform the schedule events stuff
>> > and "commit_txn" perform the assign events stuff?
>> >
>> > Does "commit time" mean the actual activation in hw_perf_enable?
>>
>> No, the idea behind hw_perf_group_sched_in() is to not perform
>> schedulability tests on each event in the group, but to add the group as
>> a whole and then perform one test.
>>
>> Of course, when that test fails, you'll have to roll-back the whole
>> group again.
>>
>> So start_txn (or a better name) would simply toggle a flag in the pmu
>> implementation that will make pmu::enable() not perform the
>> schedulablilty test.
>>
>> Then commit_txn() will perform the schedulability test (so note the
>> method has to have a !void return value, my mistake in the earlier
>> email).
>>
>> This will allow us to use the regular
>> kernel/perf_event.c::group_sched_in() and all the rollback code.
>> Currently each hw_perf_group_sched_in() implementation duplicates all
>> the rolllback code (with various bugs).
>>
>>
>>
>> We must get rid of all weak hw_perf_*() functions before we can properly
>> consider multiple struct pmu implementations.
>>
>
> Thanks for the clear explanation.
>
> Does below patch show what you mean?
>
> I only touch the x86 arch code now.
>
> ---
> arch/x86/kernel/cpu/perf_event.c | 161 +++++++++++--------------------------
> include/linux/perf_event.h | 10 ++-
> kernel/perf_event.c | 28 +++----
> 3 files changed, 67 insertions(+), 132 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 626154a..62aa9a1 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -944,6 +944,9 @@ static int x86_pmu_enable(struct perf_event *event)
> if (n < 0)
> return n;
>
> + if (!(event->pmu->flag & PERF_EVENT_TRAN_STARTED))
> + goto out;
> +
> ret = x86_pmu.schedule_events(cpuc, n, assign);
> if (ret)
> return ret;
> @@ -953,6 +956,7 @@ static int x86_pmu_enable(struct perf_event *event)
> */
> memcpy(cpuc->assign, assign, n*sizeof(int));
>
> +out:
> cpuc->n_events = n;
> cpuc->n_added += n - n0;
>
> @@ -1210,119 +1214,6 @@ x86_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
> return &unconstrained;
> }
>
> -static int x86_event_sched_in(struct perf_event *event,
> - struct perf_cpu_context *cpuctx)
> -{
> - int ret = 0;
> -
> - event->state = PERF_EVENT_STATE_ACTIVE;
> - event->oncpu = smp_processor_id();
> - event->tstamp_running += event->ctx->time - event->tstamp_stopped;
> -
> - if (!is_x86_event(event))
> - ret = event->pmu->enable(event);
> -
> - if (!ret && !is_software_event(event))
> - cpuctx->active_oncpu++;
> -
> - if (!ret && event->attr.exclusive)
> - cpuctx->exclusive = 1;
> -
> - return ret;
> -}
> -
> -static void x86_event_sched_out(struct perf_event *event,
> - struct perf_cpu_context *cpuctx)
> -{
> - event->state = PERF_EVENT_STATE_INACTIVE;
> - event->oncpu = -1;
> -
> - if (!is_x86_event(event))
> - event->pmu->disable(event);
> -
> - event->tstamp_running -= event->ctx->time - event->tstamp_stopped;
> -
> - if (!is_software_event(event))
> - cpuctx->active_oncpu--;
> -
> - if (event->attr.exclusive || !cpuctx->active_oncpu)
> - cpuctx->exclusive = 0;
> -}
> -
> -/*
> - * Called to enable a whole group of events.
> - * Returns 1 if the group was enabled, or -EAGAIN if it could not be.
> - * Assumes the caller has disabled interrupts and has
> - * frozen the PMU with hw_perf_save_disable.
> - *
> - * called with PMU disabled. If successful and return value 1,
> - * then guaranteed to call perf_enable() and hw_perf_enable()
> - */
> -int hw_perf_group_sched_in(struct perf_event *leader,
> - struct perf_cpu_context *cpuctx,
> - struct perf_event_context *ctx)
> -{
> - struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> - struct perf_event *sub;
> - int assign[X86_PMC_IDX_MAX];
> - int n0, n1, ret;
> -
> - if (!x86_pmu_initialized())
> - return 0;
> -
> - /* n0 = total number of events */
> - n0 = collect_events(cpuc, leader, true);
> - if (n0 < 0)
> - return n0;
> -
> - ret = x86_pmu.schedule_events(cpuc, n0, assign);
> - if (ret)
> - return ret;
> -
> - ret = x86_event_sched_in(leader, cpuctx);
> - if (ret)
> - return ret;
> -
> - n1 = 1;
> - list_for_each_entry(sub, &leader->sibling_list, group_entry) {
> - if (sub->state > PERF_EVENT_STATE_OFF) {
> - ret = x86_event_sched_in(sub, cpuctx);
> - if (ret)
> - goto undo;
> - ++n1;
> - }
> - }
> - /*
> - * copy new assignment, now we know it is possible
> - * will be used by hw_perf_enable()
> - */
> - memcpy(cpuc->assign, assign, n0*sizeof(int));
> -
> - cpuc->n_events = n0;
> - cpuc->n_added += n1;
> - ctx->nr_active += n1;
> -
> - /*
> - * 1 means successful and events are active
> - * This is not quite true because we defer
> - * actual activation until hw_perf_enable() but
> - * this way we* ensure caller won't try to enable
> - * individual events
> - */
> - return 1;
> -undo:
> - x86_event_sched_out(leader, cpuctx);
> - n0 = 1;
> - list_for_each_entry(sub, &leader->sibling_list, group_entry) {
> - if (sub->state == PERF_EVENT_STATE_ACTIVE) {
> - x86_event_sched_out(sub, cpuctx);
> - if (++n0 == n1)
> - break;
> - }
> - }
> - return ret;
> -}
> -
> #include "perf_event_amd.c"
> #include "perf_event_p6.c"
> #include "perf_event_p4.c"
> @@ -1454,6 +1345,47 @@ static inline void x86_pmu_read(struct perf_event *event)
> x86_perf_event_update(event);
> }
>
> +/*
> + * Set the flag to make pmu::enable() not perform the
> + * schedulablilty test.
> + */
> +static void x86_pmu_start_txn(struct pmu *pmu)
> +{
> + pmu->flag |= PERF_EVENT_TRAN_STARTED;
> +}
> +
> +static void x86_pmu_stop_txn(struct pmu *pmu)
> +{
> + pmu->flag &= ~PERF_EVENT_TRAN_STARTED;
> +}
> +
> +/*
> + * Return 0 if commit transaction success
> + */
> +static int x86_pmu_commit_txn(struct pmu *pmu)
> +{
> + struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
> + int assign[X86_PMC_IDX_MAX];
> + int n, ret;
> +
> + n = cpuc->n_events;
> +
> + if (!x86_pmu_initialized())
> + return -EAGAIN;
> +
> + ret = x86_pmu.schedule_events(cpuc, n, assign);
> + if (ret)
> + return ret;
> +
> + /*
> + * copy new assignment, now we know it is possible
> + * will be used by hw_perf_enable()
> + */
> + memcpy(cpuc->assign, assign, n*sizeof(int));
> +
> + return 0;
> +}
> +
> static const struct pmu pmu = {
> .enable = x86_pmu_enable,
> .disable = x86_pmu_disable,
> @@ -1461,6 +1393,9 @@ static const struct pmu pmu = {
> .stop = x86_pmu_stop,
> .read = x86_pmu_read,
> .unthrottle = x86_pmu_unthrottle,
> + .start_txn = x86_pmu_start_txn,
> + .stop_txn = x86_pmu_stop_txn,
> + .commit_txn = x86_pmu_commit_txn,
> };
>
> /*
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index bf896d0..93aa8d8 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -524,6 +524,8 @@ struct hw_perf_event {
>
> struct perf_event;
>
> +#define PERF_EVENT_TRAN_STARTED 1
> +
> /**
> * struct pmu - generic performance monitoring unit
> */
> @@ -534,6 +536,11 @@ struct pmu {
> void (*stop) (struct perf_event *event);
> void (*read) (struct perf_event *event);
> void (*unthrottle) (struct perf_event *event);
> + void (*start_txn) (struct pmu *pmu);
> + void (*stop_txn) (struct pmu *pmu);
> + int (*commit_txn) (struct pmu *pmu);
> +
> + u8 flag;
> };
>
> /**
> @@ -799,9 +806,6 @@ extern void perf_disable(void);
> extern void perf_enable(void);
> extern int perf_event_task_disable(void);
> extern int perf_event_task_enable(void);
> -extern int hw_perf_group_sched_in(struct perf_event *group_leader,
> - struct perf_cpu_context *cpuctx,
> - struct perf_event_context *ctx);
> extern void perf_event_update_userpage(struct perf_event *event);
> extern int perf_event_release_kernel(struct perf_event *event);
> extern struct perf_event *
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index 07b7a43..4537676 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -83,14 +83,6 @@ extern __weak const struct pmu *hw_perf_event_init(struct perf_event *event)
> void __weak hw_perf_disable(void) { barrier(); }
> void __weak hw_perf_enable(void) { barrier(); }
>
> -int __weak
> -hw_perf_group_sched_in(struct perf_event *group_leader,
> - struct perf_cpu_context *cpuctx,
> - struct perf_event_context *ctx)
> -{
> - return 0;
> -}
> -
> void __weak perf_event_print_debug(void) { }
>
> static DEFINE_PER_CPU(int, perf_disable_count);
> @@ -642,14 +634,13 @@ group_sched_in(struct perf_event *group_event,
> struct perf_event_context *ctx)
> {
> struct perf_event *event, *partial_group;
> + struct pmu *pmu = (struct pmu *)group_event->pmu;
> int ret;
>
> if (group_event->state == PERF_EVENT_STATE_OFF)
> return 0;
>
> - ret = hw_perf_group_sched_in(group_event, cpuctx, ctx);
> - if (ret)
> - return ret < 0 ? ret : 0;
> + pmu->start_txn(pmu);
>
> if (event_sched_in(group_event, cpuctx, ctx))
> return -EAGAIN;
> @@ -664,16 +655,21 @@ group_sched_in(struct perf_event *group_event,
> }
> }
>
> - return 0;
> + ret = pmu->commit_txn(pmu);
> + if (!ret) {
> + pmu->stop_txn(pmu);
> + return 0;
> + }
>
> group_error:
> + pmu->stop_txn(pmu);
> +
> /*
> - * Groups can be scheduled in as one unit only, so undo any
> - * partial group before returning:
> + * Commit transaction fails, rollback
> + * Groups can be scheduled in as one unit only, so undo
> + * whole group before returning:
> */
> list_for_each_entry(event, &group_event->sibling_list, group_entry) {
> - if (event == partial_group)
> - break;
> event_sched_out(event, cpuctx, ctx);
> }
> event_sched_out(group_event, cpuctx, ctx);
>
>
>
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