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SubjectRe: [RFC][PATCH 4/8] perf/x86: Remove PERF_X86_EVENT_COMMITTED
On Thu, Mar 14, 2019 at 6:11 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> The flag PERF_X86_EVENT_COMMITTED is used to find uncommitted events
> for which to call put_event_constraint() when scheduling fails.
>
> These are the newly added events to the list, and must form, per
> definition, the tail of cpuc->event_list[]. By computing the list
> index of the last successfull schedule, then iteration can start there
> and the flag is redundant.
>
> There are only 3 callers of x86_schedule_events(), notably:
>
> - x86_pmu_add()
> - x86_pmu_commit_txn()
> - validate_group()
>
> For x86_pmu_add(), cpuc->n_events isn't updated until after
> schedule_events() succeeds, therefore cpuc->n_events points to the
> desired index.
>
Correct.

> For x86_pmu_commit_txn(), cpuc->n_events is updated, but we can
> trivially compute the desired value with cpuc->n_txn -- the number of
> events added in this transaction.
>
I suggest you put this explanation in the code so that it is easier to
understand.

> For validate_group(), we can make the rule for x86_pmu_add() work by
> simply setting cpuc->n_events to 0 before calling schedule_events().
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Reviewed-by: Stephane Eranian <eranian@google.com>

> ---
> arch/x86/events/core.c | 21 ++++++---------------
> arch/x86/events/perf_event.h | 1 -
> 2 files changed, 6 insertions(+), 16 deletions(-)
>
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -925,19 +925,16 @@ int x86_schedule_events(struct cpu_hw_ev
> if (!unsched && assign) {
> for (i = 0; i < n; i++) {
> e = cpuc->event_list[i];
> - e->hw.flags |= PERF_X86_EVENT_COMMITTED;
> if (x86_pmu.commit_scheduling)
> x86_pmu.commit_scheduling(cpuc, i, assign[i]);
> }
> } else {
> - for (i = 0; i < n; i++) {
> + i = cpuc->n_events;
> + if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
> + i -= cpuc->n_txn;
> +
> + for (; i < n; i++) {
> e = cpuc->event_list[i];
> - /*
> - * do not put_constraint() on comitted events,
> - * because they are good to go
> - */
> - if ((e->hw.flags & PERF_X86_EVENT_COMMITTED))
> - continue;
>
> /*
> * release events that failed scheduling
> @@ -1372,11 +1369,6 @@ static void x86_pmu_del(struct perf_even
> int i;
>
> /*
> - * event is descheduled
> - */
> - event->hw.flags &= ~PERF_X86_EVENT_COMMITTED;
> -
> - /*
> * If we're called during a txn, we only need to undo x86_pmu.add.
> * The events never got scheduled and ->cancel_txn will truncate
> * the event_list.
> @@ -2079,8 +2071,7 @@ static int validate_group(struct perf_ev
> if (n < 0)
> goto out;
>
> - fake_cpuc->n_events = n;
> -
> + fake_cpuc->n_events = 0;
> ret = x86_pmu.schedule_events(fake_cpuc, n, NULL);
>
> out:
> --- a/arch/x86/events/perf_event.h
> +++ b/arch/x86/events/perf_event.h
> @@ -61,7 +61,6 @@ struct event_constraint {
> #define PERF_X86_EVENT_PEBS_LDLAT 0x0001 /* ld+ldlat data address sampling */
> #define PERF_X86_EVENT_PEBS_ST 0x0002 /* st data address sampling */
> #define PERF_X86_EVENT_PEBS_ST_HSW 0x0004 /* haswell style datala, store */
> -#define PERF_X86_EVENT_COMMITTED 0x0008 /* event passed commit_txn */

I would put a placeholder saying that bit 3 is available or renumbered
the other masks below

> #define PERF_X86_EVENT_PEBS_LD_HSW 0x0010 /* haswell style datala, load */
> #define PERF_X86_EVENT_PEBS_NA_HSW 0x0020 /* haswell style datala, unknown */
> #define PERF_X86_EVENT_EXCL 0x0040 /* HT exclusivity on counter */
>
>

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