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Date: Fri, 31 May 2013 16:21:04 +0200
From: Stephane Eranian <eranian@...gle.com>
To: Andrew Hunter <ahh@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
"mingo@...hat.com" <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] perf: reduce stack usage of schedule_events
Hi,
Any comment on this patch?
It does really help with stack pressure and will help fix a PEBS-LL issue.
Thanks.
On Thu, May 23, 2013 at 8:07 PM, Andrew Hunter <ahh@...gle.com> wrote:
> schedule_events caches event constraints on the stack during
> scheduling. Given the number of possible events, this is 512 bytes of
> stack; since it can be invoked under schedule() under god-knows-what,
> this is causing stack blowouts.
>
> Trade some space usage for stack safety: add a place to cache the
> constraint pointer to struct perf_event. For 8 bytes per event (1% of
> its size) we can save the giant stack frame.
>
> This shouldn't change any aspect of scheduling whatsoever and while in
> theory the locality's a tiny bit worse, I doubt we'll see any
> performance impact either.
>
> Tested: `perf stat whatever` does not blow up and produces
> results that aren't hugely obviously wrong. I'm not sure how to run
> particularly good tests of perf code, but this should not produce any
> functional change whatsoever.
>
> Signed-off-by: Andrew Hunter <ahh@...gle.com>
> Reviewed-by: Stephane Eranian <eranian@...gle.com>
> ---
> arch/x86/kernel/cpu/perf_event.c | 28 ++++++++++++++-------------
> arch/x86/kernel/cpu/perf_event.h | 2 +-
> arch/x86/kernel/cpu/perf_event_intel_uncore.c | 10 ++++++----
> include/linux/perf_event.h | 4 ++++
> 4 files changed, 26 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index bf0f01a..e4bfc2b 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -562,7 +562,7 @@ struct sched_state {
> struct perf_sched {
> int max_weight;
> int max_events;
> - struct event_constraint **constraints;
> + struct perf_event **events;
> struct sched_state state;
> int saved_states;
> struct sched_state saved[SCHED_STATES_MAX];
> @@ -571,7 +571,7 @@ struct perf_sched {
> /*
> * Initialize interator that runs through all events and counters.
> */
> -static void perf_sched_init(struct perf_sched *sched, struct event_constraint **c,
> +static void perf_sched_init(struct perf_sched *sched, struct perf_event **events,
> int num, int wmin, int wmax)
> {
> int idx;
> @@ -579,10 +579,10 @@ static void perf_sched_init(struct perf_sched *sched, struct event_constraint **
> memset(sched, 0, sizeof(*sched));
> sched->max_events = num;
> sched->max_weight = wmax;
> - sched->constraints = c;
> + sched->events = events;
>
> for (idx = 0; idx < num; idx++) {
> - if (c[idx]->weight == wmin)
> + if (events[idx]->hw.constraint->weight == wmin)
> break;
> }
>
> @@ -629,8 +629,7 @@ static bool __perf_sched_find_counter(struct perf_sched *sched)
> if (sched->state.event >= sched->max_events)
> return false;
>
> - c = sched->constraints[sched->state.event];
> -
> + c = sched->events[sched->state.event]->hw.constraint;
> /* Prefer fixed purpose counters */
> if (c->idxmsk64 & (~0ULL << INTEL_PMC_IDX_FIXED)) {
> idx = INTEL_PMC_IDX_FIXED;
> @@ -688,7 +687,7 @@ static bool perf_sched_next_event(struct perf_sched *sched)
> if (sched->state.weight > sched->max_weight)
> return false;
> }
> - c = sched->constraints[sched->state.event];
> + c = sched->events[sched->state.event]->hw.constraint;
> } while (c->weight != sched->state.weight);
>
> sched->state.counter = 0; /* start with first counter */
> @@ -699,12 +698,12 @@ static bool perf_sched_next_event(struct perf_sched *sched)
> /*
> * Assign a counter for each event.
> */
> -int perf_assign_events(struct event_constraint **constraints, int n,
> +int perf_assign_events(struct perf_event **events, int n,
> int wmin, int wmax, int *assign)
> {
> struct perf_sched sched;
>
> - perf_sched_init(&sched, constraints, n, wmin, wmax);
> + perf_sched_init(&sched, events, n, wmin, wmax);
>
> do {
> if (!perf_sched_find_counter(&sched))
> @@ -718,7 +717,7 @@ int perf_assign_events(struct event_constraint **constraints, int n,
>
> int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
> {
> - struct event_constraint *c, *constraints[X86_PMC_IDX_MAX];
> + struct event_constraint *c;
> unsigned long used_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
> int i, wmin, wmax, num = 0;
> struct hw_perf_event *hwc;
> @@ -726,8 +725,10 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
> bitmap_zero(used_mask, X86_PMC_IDX_MAX);
>
> for (i = 0, wmin = X86_PMC_IDX_MAX, wmax = 0; i < n; i++) {
> + hwc = &cpuc->event_list[i]->hw;
> c = x86_pmu.get_event_constraints(cpuc, cpuc->event_list[i]);
> - constraints[i] = c;
> + hwc->constraint = c;
> +
> wmin = min(wmin, c->weight);
> wmax = max(wmax, c->weight);
> }
> @@ -737,7 +738,7 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
> */
> for (i = 0; i < n; i++) {
> hwc = &cpuc->event_list[i]->hw;
> - c = constraints[i];
> + c = hwc->constraint;
>
> /* never assigned */
> if (hwc->idx == -1)
> @@ -758,7 +759,8 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
>
> /* slow path */
> if (i != n)
> - num = perf_assign_events(constraints, n, wmin, wmax, assign);
> + num = perf_assign_events(cpuc->event_list, n, wmin,
> + wmax, assign);
>
> /*
> * scheduling failed or is just a simulation,
> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
> index 7f5c75c..7a5fcd4 100644
> --- a/arch/x86/kernel/cpu/perf_event.h
> +++ b/arch/x86/kernel/cpu/perf_event.h
> @@ -483,7 +483,7 @@ static inline void __x86_pmu_enable_event(struct hw_perf_event *hwc,
>
> void x86_pmu_enable_all(int added);
>
> -int perf_assign_events(struct event_constraint **constraints, int n,
> +int perf_assign_events(struct perf_event **events, int n,
> int wmin, int wmax, int *assign);
> int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign);
>
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
> index b43200d..bf07530 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
> @@ -2058,15 +2058,16 @@ static void uncore_put_event_constraint(struct intel_uncore_box *box, struct per
> static int uncore_assign_events(struct intel_uncore_box *box, int assign[], int n)
> {
> unsigned long used_mask[BITS_TO_LONGS(UNCORE_PMC_IDX_MAX)];
> - struct event_constraint *c, *constraints[UNCORE_PMC_IDX_MAX];
> + struct event_constraint *c;
> int i, wmin, wmax, ret = 0;
> struct hw_perf_event *hwc;
>
> bitmap_zero(used_mask, UNCORE_PMC_IDX_MAX);
>
> for (i = 0, wmin = UNCORE_PMC_IDX_MAX, wmax = 0; i < n; i++) {
> + hwc = &box->event_list[i]->hw;
> c = uncore_get_event_constraint(box, box->event_list[i]);
> - constraints[i] = c;
> + hwc->constraint = c;
> wmin = min(wmin, c->weight);
> wmax = max(wmax, c->weight);
> }
> @@ -2074,7 +2075,7 @@ static int uncore_assign_events(struct intel_uncore_box *box, int assign[], int
> /* fastpath, try to reuse previous register */
> for (i = 0; i < n; i++) {
> hwc = &box->event_list[i]->hw;
> - c = constraints[i];
> + c = hwc->constraint;
>
> /* never assigned */
> if (hwc->idx == -1)
> @@ -2094,7 +2095,8 @@ static int uncore_assign_events(struct intel_uncore_box *box, int assign[], int
> }
> /* slow path */
> if (i != n)
> - ret = perf_assign_events(constraints, n, wmin, wmax, assign);
> + ret = perf_assign_events(box->event_list, n,
> + wmin, wmax, assign);
>
> if (!assign || ret) {
> for (i = 0; i < n; i++)
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 1d795df..7fcc4ab 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -114,6 +114,8 @@ struct hw_perf_event_extra {
> int idx; /* index in shared_regs->regs[] */
> };
>
> +struct event_constraint;
> +
> /**
> * struct hw_perf_event - performance event hardware details:
> */
> @@ -131,6 +133,8 @@ struct hw_perf_event {
>
> struct hw_perf_event_extra extra_reg;
> struct hw_perf_event_extra branch_reg;
> +
> + struct event_constraint *constraint;
> };
> struct { /* software */
> struct hrtimer hrtimer;
> --
> 1.8.2.1
>
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