perf/hw_breakpoint: Optimize constant number of breakpoint slots

Optimize internal hw_breakpoint state if the architecture's number of
breakpoint slots is constant. This avoids several kmalloc() calls and
potentially unnecessary failures if the allocations fail, as well as
subtly improves code generation and cache locality.

The protocol is that if an architecture defines hw_breakpoint_slots via
the preprocessor, it must be constant and the same for all types.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20220829124719.675715-7-elver@google.com

diff --git a/arch/sh/include/asm/hw_breakpoint.h b/arch/sh/include/asm/hw_breakpoint.h
index 199d17b765f2b9424d9c3eea0225260ed39b175a..361a0f57bdebda6ef10e97c6bfe708bb9a1dfbba 100644 (file)
--- a/arch/sh/include/asm/hw_breakpoint.h
+++ b/arch/sh/include/asm/hw_breakpoint.h
@@ -48,10 +48,7 @@ struct pmu;
 /* Maximum number of UBC channels */
 #define HBP_NUM                2
 
-static inline int hw_breakpoint_slots(int type)
-{
-       return HBP_NUM;
-}
+#define hw_breakpoint_slots(type) (HBP_NUM)
 
 /* arch/sh/kernel/hw_breakpoint.c */
 extern int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw);

diff --git a/arch/x86/include/asm/hw_breakpoint.h b/arch/x86/include/asm/hw_breakpoint.h
index a1f0e90d0818054c2bfb886fff380cbf336c5929..0bc931cd0698bf0214689821743088bae22e9c0a 100644 (file)
--- a/arch/x86/include/asm/hw_breakpoint.h
+++ b/arch/x86/include/asm/hw_breakpoint.h
@@ -44,10 +44,7 @@ struct arch_hw_breakpoint {
 /* Total number of available HW breakpoint registers */
 #define HBP_NUM 4
 
-static inline int hw_breakpoint_slots(int type)
-{
-       return HBP_NUM;
-}
+#define hw_breakpoint_slots(type) (HBP_NUM)
 
 struct perf_event_attr;
 struct perf_event;

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 7df46b276452e4fc23de4d3b85c1543bd89d82df..9fb66d358d81bc61ddab3b6b77f3766455cc2377 100644 (file)
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -40,13 +40,16 @@ 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 */
+#ifdef hw_breakpoint_slots
+       unsigned int    tsk_pinned[hw_breakpoint_slots(0)];
+#else
        unsigned int    *tsk_pinned;
+#endif
        /* Number of non-pinned cpu/task breakpoints in a cpu */
        unsigned int    flexible; /* XXX: placeholder, see fetch_this_slot() */
 };
 
 static DEFINE_PER_CPU(struct bp_cpuinfo, bp_cpuinfo[TYPE_MAX]);
-static int nr_slots[TYPE_MAX] __ro_after_init;
 
 static struct bp_cpuinfo *get_bp_info(int cpu, enum bp_type_idx type)
 {
@@ -73,6 +76,54 @@ struct bp_busy_slots {
 /* Serialize accesses to the above constraints */
 static DEFINE_MUTEX(nr_bp_mutex);
 
+#ifdef hw_breakpoint_slots
+/*
+ * Number of breakpoint slots is constant, and the same for all types.
+ */
+static_assert(hw_breakpoint_slots(TYPE_INST) == hw_breakpoint_slots(TYPE_DATA));
+static inline int hw_breakpoint_slots_cached(int type) { return hw_breakpoint_slots(type); }
+static inline int init_breakpoint_slots(void)          { return 0; }
+#else
+/*
+ * Dynamic number of breakpoint slots.
+ */
+static int __nr_bp_slots[TYPE_MAX] __ro_after_init;
+
+static inline int hw_breakpoint_slots_cached(int type)
+{
+       return __nr_bp_slots[type];
+}
+
+static __init int init_breakpoint_slots(void)
+{
+       int i, cpu, err_cpu;
+
+       for (i = 0; i < TYPE_MAX; i++)
+               __nr_bp_slots[i] = hw_breakpoint_slots(i);
+
+       for_each_possible_cpu(cpu) {
+               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(int), GFP_KERNEL);
+                       if (!info->tsk_pinned)
+                               goto err;
+               }
+       }
+
+       return 0;
+err:
+       for_each_possible_cpu(err_cpu) {
+               for (i = 0; i < TYPE_MAX; i++)
+                       kfree(get_bp_info(err_cpu, i)->tsk_pinned);
+               if (err_cpu == cpu)
+                       break;
+       }
+
+       return -ENOMEM;
+}
+#endif
+
 __weak int hw_breakpoint_weight(struct perf_event *bp)
 {
        return 1;
@@ -95,7 +146,7 @@ static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
        unsigned int *tsk_pinned = get_bp_info(cpu, type)->tsk_pinned;
        int i;
 
-       for (i = nr_slots[type] - 1; i >= 0; i--) {
+       for (i = hw_breakpoint_slots_cached(type) - 1; i >= 0; i--) {
                if (tsk_pinned[i] > 0)
                        return i + 1;
        }
@@ -312,7 +363,7 @@ static int __reserve_bp_slot(struct perf_event *bp, u64 bp_type)
        fetch_this_slot(&slots, weight);
 
        /* Flexible counters need to keep at least one slot */
-       if (slots.pinned + (!!slots.flexible) > nr_slots[type])
+       if (slots.pinned + (!!slots.flexible) > hw_breakpoint_slots_cached(type))
                return -ENOSPC;
 
        ret = arch_reserve_bp_slot(bp);
@@ -632,7 +683,7 @@ bool hw_breakpoint_is_used(void)
                        if (info->cpu_pinned)
                                return true;
 
-                       for (int slot = 0; slot < nr_slots[type]; ++slot) {
+                       for (int slot = 0; slot < hw_breakpoint_slots_cached(type); ++slot) {
                                if (info->tsk_pinned[slot])
                                        return true;
                        }
@@ -716,42 +767,19 @@ static struct pmu perf_breakpoint = {
 
 int __init init_hw_breakpoint(void)
 {
-       int cpu, err_cpu;
-       int i, ret;
-
-       for (i = 0; i < TYPE_MAX; i++)
-               nr_slots[i] = hw_breakpoint_slots(i);
-
-       for_each_possible_cpu(cpu) {
-               for (i = 0; i < TYPE_MAX; i++) {
-                       struct bp_cpuinfo *info = get_bp_info(cpu, i);
-
-                       info->tsk_pinned = kcalloc(nr_slots[i], sizeof(int),
-                                                       GFP_KERNEL);
-                       if (!info->tsk_pinned) {
-                               ret = -ENOMEM;
-                               goto err;
-                       }
-               }
-       }
+       int ret;
 
        ret = rhltable_init(&task_bps_ht, &task_bps_ht_params);
        if (ret)
-               goto err;
+               return ret;
+
+       ret = init_breakpoint_slots();
+       if (ret)
+               return ret;
 
        constraints_initialized = true;
 
        perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
 
        return register_die_notifier(&hw_breakpoint_exceptions_nb);
-
-err:
-       for_each_possible_cpu(err_cpu) {
-               for (i = 0; i < TYPE_MAX; i++)
-                       kfree(get_bp_info(err_cpu, i)->tsk_pinned);
-               if (err_cpu == cpu)
-                       break;
-       }
-
-       return ret;
 }