| Message ID | 20220704150514.48816-13-elver@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | perf/hw_breakpoint: Optimize for thousands of tasks | expand |
On Mon, Jul 4, 2022 at 8:07 AM Marco Elver <elver@google.com> wrote: > > Factor out the existing `atomic_t count[N]` into its own struct called > 'bp_slots_histogram', to generalize and make its intent clearer in > preparation of reusing elsewhere. The basic idea of bucketing "total > uses of N slots" resembles a histogram, so calling it such seems most > intuitive. > > No functional change. > > Signed-off-by: Marco Elver <elver@google.com> > Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Acked-by: Ian Rogers <irogers@google.com> Thanks, Ian > --- > v3: > * Also warn in bp_slots_histogram_add() if count goes below 0. > > v2: > * New patch. > --- > kernel/events/hw_breakpoint.c | 96 +++++++++++++++++++++++------------ > 1 file changed, 63 insertions(+), 33 deletions(-) > > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c > index 229c6f4fae75..03ebecf048c0 100644 > --- a/kernel/events/hw_breakpoint.c > +++ b/kernel/events/hw_breakpoint.c > @@ -36,19 +36,27 @@ > #include <linux/slab.h> > > /* > - * Constraints data > + * Datastructure to track the total uses of N slots across tasks or CPUs; > + * bp_slots_histogram::count[N] is the number of assigned N+1 breakpoint slots. > */ > -struct bp_cpuinfo { > - /* Number of pinned cpu breakpoints in a cpu */ > - unsigned int cpu_pinned; > - /* tsk_pinned[n] is the number of tasks having n+1 breakpoints */ > +struct bp_slots_histogram { > #ifdef hw_breakpoint_slots > - atomic_t tsk_pinned[hw_breakpoint_slots(0)]; > + atomic_t count[hw_breakpoint_slots(0)]; > #else > - atomic_t *tsk_pinned; > + atomic_t *count; > #endif > }; > > +/* > + * Per-CPU constraints data. > + */ > +struct bp_cpuinfo { > + /* Number of pinned CPU breakpoints in a CPU. */ > + unsigned int cpu_pinned; > + /* Histogram of pinned task breakpoints in a CPU. */ > + struct bp_slots_histogram tsk_pinned; > +}; > + > static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]); > > static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type) > @@ -159,6 +167,18 @@ static inline int hw_breakpoint_slots_cached(int type) > return __nr_bp_slots[type]; > } > > +static __init bool > +bp_slots_histogram_alloc(struct bp_slots_histogram *hist, enum bp_type_idx type) > +{ > + hist->count = kcalloc(hw_breakpoint_slots_cached(type), sizeof(*hist->count), GFP_KERNEL); > + return hist->count; > +} > + > +static __init void bp_slots_histogram_free(struct bp_slots_histogram *hist) > +{ > + kfree(hist->count); > +} > + > static __init int init_breakpoint_slots(void) > { > int i, cpu, err_cpu; > @@ -170,8 +190,7 @@ static __init int init_breakpoint_slots(void) > for (i = 0; i < TYPE_MAX; i++) { > struct bp_cpuinfo *info = get_bp_info(cpu, i); > > - info->tsk_pinned = kcalloc(__nr_bp_slots[i], sizeof(atomic_t), GFP_KERNEL); > - if (!info->tsk_pinned) > + if (!bp_slots_histogram_alloc(&info->tsk_pinned, i)) > goto err; > } > } > @@ -180,7 +199,7 @@ static __init int init_breakpoint_slots(void) > err: > for_each_possible_cpu(err_cpu) { > for (i = 0; i < TYPE_MAX; i++) > - kfree(get_bp_info(err_cpu, i)->tsk_pinned); > + bp_slots_histogram_free(&get_bp_info(err_cpu, i)->tsk_pinned); > if (err_cpu == cpu) > break; > } > @@ -189,6 +208,34 @@ static __init int init_breakpoint_slots(void) > } > #endif > > +static inline void > +bp_slots_histogram_add(struct bp_slots_histogram *hist, int old, int val) > +{ > + const int old_idx = old - 1; > + const int new_idx = old_idx + val; > + > + if (old_idx >= 0) > + WARN_ON(atomic_dec_return_relaxed(&hist->count[old_idx]) < 0); > + if (new_idx >= 0) > + WARN_ON(atomic_inc_return_relaxed(&hist->count[new_idx]) < 0); > +} > + > +static int > +bp_slots_histogram_max(struct bp_slots_histogram *hist, enum bp_type_idx type) > +{ > + for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) { > + const int count = atomic_read(&hist->count[i]); > + > + /* Catch unexpected writers; we want a stable snapshot. */ > + ASSERT_EXCLUSIVE_WRITER(hist->count[i]); > + if (count > 0) > + return i + 1; > + WARN(count < 0, "inconsistent breakpoint slots histogram"); > + } > + > + return 0; > +} > + > #ifndef hw_breakpoint_weight > static inline int hw_breakpoint_weight(struct perf_event *bp) > { > @@ -205,13 +252,11 @@ static inline enum bp_type_idx find_slot_idx(u64 bp_type) > } > > /* > - * Report the maximum number of pinned breakpoints a task > - * have in this cpu > + * Return the maximum number of pinned breakpoints a task has in this CPU. > */ > static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type) > { > - atomic_t *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned; > - int i; > + struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned; > > /* > * At this point we want to have acquired the bp_cpuinfo_sem as a > @@ -219,14 +264,7 @@ static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type) > * toggle_bp_task_slot() to tsk_pinned, and we get a stable snapshot. > */ > lockdep_assert_held_write(&bp_cpuinfo_sem); > - > - for (i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) { > - ASSERT_EXCLUSIVE_WRITER(tsk_pinned[i]); /* Catch unexpected writers. */ > - if (atomic_read(&tsk_pinned[i]) > 0) > - return i + 1; > - } > - > - return 0; > + return bp_slots_histogram_max(tsk_pinned, type); > } > > /* > @@ -300,8 +338,7 @@ max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type) > static void toggle_bp_task_slot(struct perf_event *bp, int cpu, > enum bp_type_idx type, int weight) > { > - atomic_t *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned; > - int old_idx, new_idx; > + struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned; > > /* > * If bp->hw.target, tsk_pinned is only modified, but not used > @@ -311,14 +348,7 @@ static void toggle_bp_task_slot(struct perf_event *bp, int cpu, > * bp_cpuinfo_sem as a writer to stabilize tsk_pinned's value. > */ > lockdep_assert_held_read(&bp_cpuinfo_sem); > - > - old_idx = task_bp_pinned(cpu, bp, type) - 1; > - new_idx = old_idx + weight; > - > - if (old_idx >= 0) > - atomic_dec(&tsk_pinned[old_idx]); > - if (new_idx >= 0) > - atomic_inc(&tsk_pinned[new_idx]); > + bp_slots_histogram_add(tsk_pinned, task_bp_pinned(cpu, bp, type), weight); > } > > /* > @@ -768,7 +798,7 @@ bool hw_breakpoint_is_used(void) > return true; > > for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) { > - if (atomic_read(&info->tsk_pinned[slot])) > + if (atomic_read(&info->tsk_pinned.count[slot])) > return true; > } > } > -- > 2.37.0.rc0.161.g10f37bed90-goog >
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c index 229c6f4fae75..03ebecf048c0 100644 --- a/kernel/events/hw_breakpoint.c +++ b/kernel/events/hw_breakpoint.c @@ -36,19 +36,27 @@ #include <linux/slab.h> /* - * Constraints data + * Datastructure to track the total uses of N slots across tasks or CPUs; + * bp_slots_histogram::count[N] is the number of assigned N+1 breakpoint slots. */ -struct bp_cpuinfo { - /* Number of pinned cpu breakpoints in a cpu */ - unsigned int cpu_pinned; - /* tsk_pinned[n] is the number of tasks having n+1 breakpoints */ +struct bp_slots_histogram { #ifdef hw_breakpoint_slots - atomic_t tsk_pinned[hw_breakpoint_slots(0)]; + atomic_t count[hw_breakpoint_slots(0)]; #else - atomic_t *tsk_pinned; + atomic_t *count; #endif }; +/* + * Per-CPU constraints data. + */ +struct bp_cpuinfo { + /* Number of pinned CPU breakpoints in a CPU. */ + unsigned int cpu_pinned; + /* Histogram of pinned task breakpoints in a CPU. */ + struct bp_slots_histogram tsk_pinned; +}; + static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]); static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type) @@ -159,6 +167,18 @@ static inline int hw_breakpoint_slots_cached(int type) return __nr_bp_slots[type]; } +static __init bool +bp_slots_histogram_alloc(struct bp_slots_histogram *hist, enum bp_type_idx type) +{ + hist->count = kcalloc(hw_breakpoint_slots_cached(type), sizeof(*hist->count), GFP_KERNEL); + return hist->count; +} + +static __init void bp_slots_histogram_free(struct bp_slots_histogram *hist) +{ + kfree(hist->count); +} + static __init int init_breakpoint_slots(void) { int i, cpu, err_cpu; @@ -170,8 +190,7 @@ static __init int init_breakpoint_slots(void) for (i = 0; i < TYPE_MAX; i++) { struct bp_cpuinfo *info = get_bp_info(cpu, i); - info->tsk_pinned = kcalloc(__nr_bp_slots[i], sizeof(atomic_t), GFP_KERNEL); - if (!info->tsk_pinned) + if (!bp_slots_histogram_alloc(&info->tsk_pinned, i)) goto err; } } @@ -180,7 +199,7 @@ static __init int init_breakpoint_slots(void) err: for_each_possible_cpu(err_cpu) { for (i = 0; i < TYPE_MAX; i++) - kfree(get_bp_info(err_cpu, i)->tsk_pinned); + bp_slots_histogram_free(&get_bp_info(err_cpu, i)->tsk_pinned); if (err_cpu == cpu) break; } @@ -189,6 +208,34 @@ static __init int init_breakpoint_slots(void) } #endif +static inline void +bp_slots_histogram_add(struct bp_slots_histogram *hist, int old, int val) +{ + const int old_idx = old - 1; + const int new_idx = old_idx + val; + + if (old_idx >= 0) + WARN_ON(atomic_dec_return_relaxed(&hist->count[old_idx]) < 0); + if (new_idx >= 0) + WARN_ON(atomic_inc_return_relaxed(&hist->count[new_idx]) < 0); +} + +static int +bp_slots_histogram_max(struct bp_slots_histogram *hist, enum bp_type_idx type) +{ + for (int i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) { + const int count = atomic_read(&hist->count[i]); + + /* Catch unexpected writers; we want a stable snapshot. */ + ASSERT_EXCLUSIVE_WRITER(hist->count[i]); + if (count > 0) + return i + 1; + WARN(count < 0, "inconsistent breakpoint slots histogram"); + } + + return 0; +} + #ifndef hw_breakpoint_weight static inline int hw_breakpoint_weight(struct perf_event *bp) { @@ -205,13 +252,11 @@ static inline enum bp_type_idx find_slot_idx(u64 bp_type) } /* - * Report the maximum number of pinned breakpoints a task - * have in this cpu + * Return the maximum number of pinned breakpoints a task has in this CPU. */ static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type) { - atomic_t *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned; - int i; + struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned; /* * At this point we want to have acquired the bp_cpuinfo_sem as a @@ -219,14 +264,7 @@ static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type) * toggle_bp_task_slot() to tsk_pinned, and we get a stable snapshot. */ lockdep_assert_held_write(&bp_cpuinfo_sem); - - for (i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) { - ASSERT_EXCLUSIVE_WRITER(tsk_pinned[i]); /* Catch unexpected writers. */ - if (atomic_read(&tsk_pinned[i]) > 0) - return i + 1; - } - - return 0; + return bp_slots_histogram_max(tsk_pinned, type); } /* @@ -300,8 +338,7 @@ max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type) static void toggle_bp_task_slot(struct perf_event *bp, int cpu, enum bp_type_idx type, int weight) { - atomic_t *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned; - int old_idx, new_idx; + struct bp_slots_histogram *tsk_pinned = &get_bp_info(cpu, type)->tsk_pinned; /* * If bp->hw.target, tsk_pinned is only modified, but not used @@ -311,14 +348,7 @@ static void toggle_bp_task_slot(struct perf_event *bp, int cpu, * bp_cpuinfo_sem as a writer to stabilize tsk_pinned's value. */ lockdep_assert_held_read(&bp_cpuinfo_sem); - - old_idx = task_bp_pinned(cpu, bp, type) - 1; - new_idx = old_idx + weight; - - if (old_idx >= 0) - atomic_dec(&tsk_pinned[old_idx]); - if (new_idx >= 0) - atomic_inc(&tsk_pinned[new_idx]); + bp_slots_histogram_add(tsk_pinned, task_bp_pinned(cpu, bp, type), weight); } /* @@ -768,7 +798,7 @@ bool hw_breakpoint_is_used(void) return true; for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) { - if (atomic_read(&info->tsk_pinned[slot])) + if (atomic_read(&info->tsk_pinned.count[slot])) return true; } }