| Message ID | 20220628095833.2579903-13-elver@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | perf/hw_breakpoint: Optimize for thousands of tasks | expand |
On Tue, 28 Jun 2022 at 11:59, Marco Elver <elver@google.com> wrote: > > Running the perf benchmark with (note: more aggressive parameters vs. > preceding changes, but same 256 CPUs host): > > | $> perf bench -r 100 breakpoint thread -b 4 -p 128 -t 512 > | # Running 'breakpoint/thread' benchmark: > | # Created/joined 100 threads with 4 breakpoints and 128 parallelism > | Total time: 1.989 [sec] > | > | 38.854160 usecs/op > | 4973.332500 usecs/op/cpu > > 20.43% [kernel] [k] queued_spin_lock_slowpath > 18.75% [kernel] [k] osq_lock > 16.98% [kernel] [k] rhashtable_jhash2 > 8.34% [kernel] [k] task_bp_pinned > 4.23% [kernel] [k] smp_cfm_core_cond > 3.65% [kernel] [k] bcmp > 2.83% [kernel] [k] toggle_bp_slot > 1.87% [kernel] [k] find_next_bit > 1.49% [kernel] [k] __reserve_bp_slot > > We can see that a majority of the time is now spent hashing task > pointers to index into task_bps_ht in task_bp_pinned(). > > Obtaining the max_bp_pinned_slots() for CPU-independent task targets > currently is O(#cpus), and calls task_bp_pinned() for each CPU, even if > the result of task_bp_pinned() is CPU-independent. > > The loop in max_bp_pinned_slots() wants to compute the maximum slots > across all CPUs. If task_bp_pinned() is CPU-independent, we can do so by > obtaining the max slots across all CPUs and adding task_bp_pinned(). > > To do so in O(1), use a bp_slots_histogram for CPU-pinned slots. > > After this optimization: > > | $> perf bench -r 100 breakpoint thread -b 4 -p 128 -t 512 > | # Running 'breakpoint/thread' benchmark: > | # Created/joined 100 threads with 4 breakpoints and 128 parallelism > | Total time: 1.930 [sec] > | > | 37.697832 usecs/op > | 4825.322500 usecs/op/cpu > > 19.13% [kernel] [k] queued_spin_lock_slowpath > 18.21% [kernel] [k] rhashtable_jhash2 > 15.46% [kernel] [k] osq_lock > 6.27% [kernel] [k] toggle_bp_slot > 5.91% [kernel] [k] task_bp_pinned > 5.05% [kernel] [k] smp_cfm_core_cond > 1.78% [kernel] [k] update_sg_lb_stats > 1.36% [kernel] [k] llist_reverse_order > 1.34% [kernel] [k] find_next_bit > 1.19% [kernel] [k] bcmp > > Suggesting that time spent in task_bp_pinned() has been reduced. > However, we're still hashing too much, which will be addressed in the > subsequent change. > > Signed-off-by: Marco Elver <elver@google.com> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> > --- > v2: > * New patch. > --- > kernel/events/hw_breakpoint.c | 45 +++++++++++++++++++++++++++++++---- > 1 file changed, 41 insertions(+), 4 deletions(-) > > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c > index 18886f115abc..b5180a2ccfbf 100644 > --- a/kernel/events/hw_breakpoint.c > +++ b/kernel/events/hw_breakpoint.c > @@ -64,6 +64,9 @@ static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type) > return per_cpu_ptr(bp_cpuinfo + type, cpu); > } > > +/* Number of pinned CPU breakpoints globally. */ > +static struct bp_slots_histogram cpu_pinned[TYPE_MAX]; > + > /* Keep track of the breakpoints attached to tasks */ > static struct rhltable task_bps_ht; > static const struct rhashtable_params task_bps_ht_params = { > @@ -194,6 +197,10 @@ static __init int init_breakpoint_slots(void) > goto err; > } > } > + for (i = 0; i < TYPE_MAX; i++) { > + if (!bp_slots_histogram_alloc(&cpu_pinned[i], i)) > + goto err; > + } > > return 0; > err: > @@ -203,6 +210,8 @@ static __init int init_breakpoint_slots(void) > if (err_cpu == cpu) > break; > } > + for (i = 0; i < TYPE_MAX; i++) > + bp_slots_histogram_free(&cpu_pinned[i]); > > return -ENOMEM; > } > @@ -270,6 +279,9 @@ static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type) > /* > * Count the number of breakpoints of the same type and same task. > * The given event must be not on the list. > + * > + * If @cpu is -1, but the result of task_bp_pinned() is not CPU-independent, > + * returns a negative value. > */ > static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type) > { > @@ -288,9 +300,18 @@ static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type) > goto out; > > rhl_for_each_entry_rcu(iter, pos, head, hw.bp_list) { > - if (find_slot_idx(iter->attr.bp_type) == type && > - (iter->cpu < 0 || cpu == iter->cpu)) > - count += hw_breakpoint_weight(iter); > + if (find_slot_idx(iter->attr.bp_type) != type) > + continue; > + > + if (iter->cpu >= 0) { > + if (cpu == -1) { > + count = -1; > + goto out; > + } else if (cpu != iter->cpu) > + continue; > + } > + > + count += hw_breakpoint_weight(iter); > } > > out: > @@ -316,6 +337,19 @@ max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type) > int pinned_slots = 0; > int cpu; > > + if (bp->hw.target && bp->cpu < 0) { > + int max_pinned = task_bp_pinned(-1, bp, type); > + > + if (max_pinned >= 0) { > + /* > + * Fast path: task_bp_pinned() is CPU-independent and > + * returns the same value for any CPU. > + */ > + max_pinned += bp_slots_histogram_max(&cpu_pinned[type], type); > + return max_pinned; > + } > + } > + > for_each_cpu(cpu, cpumask) { > struct bp_cpuinfo *info = get_bp_info(cpu, type); > int nr; > @@ -366,8 +400,11 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type, > > /* Pinned counter cpu profiling */ > if (!bp->hw.target) { > + struct bp_cpuinfo *info = get_bp_info(bp->cpu, type); > + > lockdep_assert_held_write(&bp_cpuinfo_sem); > - get_bp_info(bp->cpu, type)->cpu_pinned += weight; > + bp_slots_histogram_add(&cpu_pinned[type], info->cpu_pinned, weight); > + info->cpu_pinned += weight; > return 0; > } > > -- > 2.37.0.rc0.161.g10f37bed90-goog >
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c index 18886f115abc..b5180a2ccfbf 100644 --- a/kernel/events/hw_breakpoint.c +++ b/kernel/events/hw_breakpoint.c @@ -64,6 +64,9 @@ static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type) return per_cpu_ptr(bp_cpuinfo + type, cpu); } +/* Number of pinned CPU breakpoints globally. */ +static struct bp_slots_histogram cpu_pinned[TYPE_MAX]; + /* Keep track of the breakpoints attached to tasks */ static struct rhltable task_bps_ht; static const struct rhashtable_params task_bps_ht_params = { @@ -194,6 +197,10 @@ static __init int init_breakpoint_slots(void) goto err; } } + for (i = 0; i < TYPE_MAX; i++) { + if (!bp_slots_histogram_alloc(&cpu_pinned[i], i)) + goto err; + } return 0; err: @@ -203,6 +210,8 @@ static __init int init_breakpoint_slots(void) if (err_cpu == cpu) break; } + for (i = 0; i < TYPE_MAX; i++) + bp_slots_histogram_free(&cpu_pinned[i]); return -ENOMEM; } @@ -270,6 +279,9 @@ static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type) /* * Count the number of breakpoints of the same type and same task. * The given event must be not on the list. + * + * If @cpu is -1, but the result of task_bp_pinned() is not CPU-independent, + * returns a negative value. */ static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type) { @@ -288,9 +300,18 @@ static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type) goto out; rhl_for_each_entry_rcu(iter, pos, head, hw.bp_list) { - if (find_slot_idx(iter->attr.bp_type) == type && - (iter->cpu < 0 || cpu == iter->cpu)) - count += hw_breakpoint_weight(iter); + if (find_slot_idx(iter->attr.bp_type) != type) + continue; + + if (iter->cpu >= 0) { + if (cpu == -1) { + count = -1; + goto out; + } else if (cpu != iter->cpu) + continue; + } + + count += hw_breakpoint_weight(iter); } out: @@ -316,6 +337,19 @@ max_bp_pinned_slots(struct perf_event *bp, enum bp_type_idx type) int pinned_slots = 0; int cpu; + if (bp->hw.target && bp->cpu < 0) { + int max_pinned = task_bp_pinned(-1, bp, type); + + if (max_pinned >= 0) { + /* + * Fast path: task_bp_pinned() is CPU-independent and + * returns the same value for any CPU. + */ + max_pinned += bp_slots_histogram_max(&cpu_pinned[type], type); + return max_pinned; + } + } + for_each_cpu(cpu, cpumask) { struct bp_cpuinfo *info = get_bp_info(cpu, type); int nr; @@ -366,8 +400,11 @@ toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type, /* Pinned counter cpu profiling */ if (!bp->hw.target) { + struct bp_cpuinfo *info = get_bp_info(bp->cpu, type); + lockdep_assert_held_write(&bp_cpuinfo_sem); - get_bp_info(bp->cpu, type)->cpu_pinned += weight; + bp_slots_histogram_add(&cpu_pinned[type], info->cpu_pinned, weight); + info->cpu_pinned += weight; return 0; }
Running the perf benchmark with (note: more aggressive parameters vs. preceding changes, but same 256 CPUs host): | $> perf bench -r 100 breakpoint thread -b 4 -p 128 -t 512 | # Running 'breakpoint/thread' benchmark: | # Created/joined 100 threads with 4 breakpoints and 128 parallelism | Total time: 1.989 [sec] | | 38.854160 usecs/op | 4973.332500 usecs/op/cpu 20.43% [kernel] [k] queued_spin_lock_slowpath 18.75% [kernel] [k] osq_lock 16.98% [kernel] [k] rhashtable_jhash2 8.34% [kernel] [k] task_bp_pinned 4.23% [kernel] [k] smp_cfm_core_cond 3.65% [kernel] [k] bcmp 2.83% [kernel] [k] toggle_bp_slot 1.87% [kernel] [k] find_next_bit 1.49% [kernel] [k] __reserve_bp_slot We can see that a majority of the time is now spent hashing task pointers to index into task_bps_ht in task_bp_pinned(). Obtaining the max_bp_pinned_slots() for CPU-independent task targets currently is O(#cpus), and calls task_bp_pinned() for each CPU, even if the result of task_bp_pinned() is CPU-independent. The loop in max_bp_pinned_slots() wants to compute the maximum slots across all CPUs. If task_bp_pinned() is CPU-independent, we can do so by obtaining the max slots across all CPUs and adding task_bp_pinned(). To do so in O(1), use a bp_slots_histogram for CPU-pinned slots. After this optimization: | $> perf bench -r 100 breakpoint thread -b 4 -p 128 -t 512 | # Running 'breakpoint/thread' benchmark: | # Created/joined 100 threads with 4 breakpoints and 128 parallelism | Total time: 1.930 [sec] | | 37.697832 usecs/op | 4825.322500 usecs/op/cpu 19.13% [kernel] [k] queued_spin_lock_slowpath 18.21% [kernel] [k] rhashtable_jhash2 15.46% [kernel] [k] osq_lock 6.27% [kernel] [k] toggle_bp_slot 5.91% [kernel] [k] task_bp_pinned 5.05% [kernel] [k] smp_cfm_core_cond 1.78% [kernel] [k] update_sg_lb_stats 1.36% [kernel] [k] llist_reverse_order 1.34% [kernel] [k] find_next_bit 1.19% [kernel] [k] bcmp Suggesting that time spent in task_bp_pinned() has been reduced. However, we're still hashing too much, which will be addressed in the subsequent change. Signed-off-by: Marco Elver <elver@google.com> --- v2: * New patch. --- kernel/events/hw_breakpoint.c | 45 +++++++++++++++++++++++++++++++---- 1 file changed, 41 insertions(+), 4 deletions(-)