On Wed, 2010-04-21 at 16:32 +0800, stephane eranian wrote:
quoted text
> 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.

Do you mean the pmu->flag?

You are right, pmu->flag should be per cpu data.

Will update the patch.

Thanks,
Lin Ming

quoted text
> 
> 
> On Wed, Apr 21, 2010 at 10:08 AM, Lin Ming <ming.m.lin@intel.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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