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Subject[PATCH 1/3] perf_events: update Intel extra regs shared constraints management (v3)

This patch improves the code managing the extra shared registers
used for offcore_response events on Intel Nehalem/Westmere. The
idea is to use static allocation instead of dynamic allocation.
This simplifies greatly the get and put constraint routines for
those events.

The patch also renames per_core to shared_regs because the same
data structure gets used whether or not HT is on. When HT is
off, those events still need to coordination because they use
a extra MSR that has to be shared within an event group.

The first post of this patch had an older (bogus) version of
the patch with bogus initialization of reg->idx.

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

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 3a0338b..0f8d3ff 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -45,6 +45,29 @@ do { \
#endif

/*
+ * | NHM/WSM | SNB |
+ * register -------------------------------
+ * | HT | no HT | HT | no HT |
+ *-----------------------------------------
+ * offcore | core | core | cpu | core |
+ * lbr_sel | core | core | cpu | core |
+ * ld_lat | cpu | core | cpu | core |
+ *-----------------------------------------
+ *
+ * Given that there is a small number of shared regs,
+ * we can pre-allocate their slot in the per-cpu
+ * per-core reg tables.
+ */
+enum extra_reg_type {
+ EXTRA_REG_NONE = -1, /* not used */
+
+ EXTRA_REG_RSP_0 = 0, /* offcore_response_0 */
+ EXTRA_REG_RSP_1 = 1, /* offcore_response_1 */
+
+ EXTRA_REG_MAX /* number of entries needed */
+};
+
+/*
* best effort, GUP based copy_from_user() that assumes IRQ or NMI context
*/
static unsigned long
@@ -132,11 +155,10 @@ struct cpu_hw_events {
struct perf_branch_entry lbr_entries[MAX_LBR_ENTRIES];

/*
- * Intel percore register state.
- * Coordinate shared resources between HT threads.
+ * manage shared (per-core, per-cpu) registers
+ * used on Intel NHM/WSM/SNB
*/
- int percore_used; /* Used by this CPU? */
- struct intel_percore *per_core;
+ struct intel_shared_regs *shared_regs;

/*
* AMD specific bits
@@ -187,26 +209,45 @@ struct cpu_hw_events {
for ((e) = (c); (e)->weight; (e)++)

/*
+ * Per register state.
+ */
+struct er_account {
+ raw_spinlock_t lock; /* per-core: protect structure */
+ u64 config; /* extra MSR config */
+ u64 reg; /* extra MSR number */
+ atomic_t ref; /* reference count */
+};
+
+/*
* Extra registers for specific events.
+ *
* Some events need large masks and require external MSRs.
- * Define a mapping to these extra registers.
+ * Those extra MSRs end up being shared for all events on
+ * a PMU and sometimes between PMU of sibling HT threads.
+ * In either case, the kernel needs to handle conflicting
+ * accesses to those extra, shared, regs. The data structure
+ * to manage those registers is stored in cpu_hw_event.
*/
struct extra_reg {
unsigned int event;
unsigned int msr;
u64 config_mask;
u64 valid_mask;
+ int idx; /* per_xxx->regs[] reg index */
};

-#define EVENT_EXTRA_REG(e, ms, m, vm) { \
+#define EVENT_EXTRA_REG(e, ms, m, vm, i) { \
.event = (e), \
.msr = (ms), \
.config_mask = (m), \
.valid_mask = (vm), \
+ .idx = EXTRA_REG_##i \
}
-#define INTEL_EVENT_EXTRA_REG(event, msr, vm) \
- EVENT_EXTRA_REG(event, msr, ARCH_PERFMON_EVENTSEL_EVENT, vm)
-#define EVENT_EXTRA_END EVENT_EXTRA_REG(0, 0, 0, 0)
+
+#define INTEL_EVENT_EXTRA_REG(event, msr, vm, idx) \
+ EVENT_EXTRA_REG(event, msr, ARCH_PERFMON_EVENTSEL_EVENT, vm, idx)
+
+#define EVENT_EXTRA_END EVENT_EXTRA_REG(0, 0, 0, 0, RSP_0)

union perf_capabilities {
struct {
@@ -252,7 +293,6 @@ struct x86_pmu {
void (*put_event_constraints)(struct cpu_hw_events *cpuc,
struct perf_event *event);
struct event_constraint *event_constraints;
- struct event_constraint *percore_constraints;
void (*quirks)(void);
int perfctr_second_write;

@@ -393,10 +433,10 @@ static inline unsigned int x86_pmu_event_addr(int index)
*/
static int x86_pmu_extra_regs(u64 config, struct perf_event *event)
{
+ struct hw_perf_event_extra *reg;
struct extra_reg *er;

- event->hw.extra_reg = 0;
- event->hw.extra_config = 0;
+ reg = &event->hw.extra_reg;

if (!x86_pmu.extra_regs)
return 0;
@@ -406,8 +446,10 @@ static int x86_pmu_extra_regs(u64 config, struct perf_event *event)
continue;
if (event->attr.config1 & ~er->valid_mask)
return -EINVAL;
- event->hw.extra_reg = er->msr;
- event->hw.extra_config = event->attr.config1;
+
+ reg->idx = er->idx;
+ reg->config = event->attr.config1;
+ reg->reg = er->msr;
break;
}
return 0;
@@ -706,6 +748,9 @@ static int __x86_pmu_event_init(struct perf_event *event)
event->hw.last_cpu = -1;
event->hw.last_tag = ~0ULL;

+ /* mark unused */
+ event->hw.extra_reg.idx = EXTRA_REG_NONE;
+
return x86_pmu.hw_config(event);
}

@@ -747,8 +792,8 @@ static void x86_pmu_disable(struct pmu *pmu)
static inline void __x86_pmu_enable_event(struct hw_perf_event *hwc,
u64 enable_mask)
{
- if (hwc->extra_reg)
- wrmsrl(hwc->extra_reg, hwc->extra_config);
+ if (hwc->extra_reg.reg)
+ wrmsrl(hwc->extra_reg.reg, hwc->extra_reg.config);
wrmsrl(hwc->config_base, hwc->config | enable_mask);
}

@@ -1685,7 +1730,6 @@ static int validate_group(struct perf_event *event)
fake_cpuc = kmalloc(sizeof(*fake_cpuc), GFP_KERNEL | __GFP_ZERO);
if (!fake_cpuc)
goto out;
-
/*
* the event is not yet connected with its
* siblings therefore we must first collect
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 41178c8..2d40f33 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1,25 +1,15 @@
#ifdef CONFIG_CPU_SUP_INTEL

-#define MAX_EXTRA_REGS 2
-
-/*
- * Per register state.
- */
-struct er_account {
- int ref; /* reference count */
- unsigned int extra_reg; /* extra MSR number */
- u64 extra_config; /* extra MSR config */
-};
-
/*
- * Per core state
- * This used to coordinate shared registers for HT threads.
+ * Per core/cpu state
+ *
+ * Used to coordinate shared registers between HT threads or
+ * among events on a single PMU.
*/
-struct intel_percore {
- raw_spinlock_t lock; /* protect structure */
- struct er_account regs[MAX_EXTRA_REGS];
- int refcnt; /* number of threads */
- unsigned core_id;
+struct intel_shared_regs {
+ struct er_account regs[EXTRA_REG_MAX];
+ int refcnt; /* per-core: #HT threads */
+ unsigned core_id; /* per-core: core id */
};

/*
@@ -88,16 +78,10 @@ static struct event_constraint intel_nehalem_event_constraints[] __read_mostly =

static struct extra_reg intel_nehalem_extra_regs[] __read_mostly =
{
- INTEL_EVENT_EXTRA_REG(0xb7, MSR_OFFCORE_RSP_0, 0xffff),
+ INTEL_EVENT_EXTRA_REG(0xb7, MSR_OFFCORE_RSP_0, 0xffff, RSP_0),
EVENT_EXTRA_END
};

-static struct event_constraint intel_nehalem_percore_constraints[] __read_mostly =
-{
- INTEL_EVENT_CONSTRAINT(0xb7, 0),
- EVENT_CONSTRAINT_END
-};
-
static struct event_constraint intel_westmere_event_constraints[] __read_mostly =
{
FIXED_EVENT_CONSTRAINT(0x00c0, 0), /* INST_RETIRED.ANY */
@@ -125,18 +109,11 @@ static struct event_constraint intel_snb_event_constraints[] __read_mostly =

static struct extra_reg intel_westmere_extra_regs[] __read_mostly =
{
- INTEL_EVENT_EXTRA_REG(0xb7, MSR_OFFCORE_RSP_0, 0xffff),
- INTEL_EVENT_EXTRA_REG(0xbb, MSR_OFFCORE_RSP_1, 0xffff),
+ INTEL_EVENT_EXTRA_REG(0xb7, MSR_OFFCORE_RSP_0, 0xffff, RSP_0),
+ INTEL_EVENT_EXTRA_REG(0xbb, MSR_OFFCORE_RSP_1, 0xffff, RSP_1),
EVENT_EXTRA_END
};

-static struct event_constraint intel_westmere_percore_constraints[] __read_mostly =
-{
- INTEL_EVENT_CONSTRAINT(0xb7, 0),
- INTEL_EVENT_CONSTRAINT(0xbb, 0),
- EVENT_CONSTRAINT_END
-};
-
static struct event_constraint intel_gen_event_constraints[] __read_mostly =
{
FIXED_EVENT_CONSTRAINT(0x00c0, 0), /* INST_RETIRED.ANY */
@@ -1037,67 +1014,91 @@ intel_bts_constraints(struct perf_event *event)
return NULL;
}

+/*
+ * manage allocation of shared extra msr for certain events
+ *
+ * sharing can be:
+ * per-cpu: to be shared between the various events on a single PMU
+ * per-core: per-cpu + shared by HT threads
+ */
static struct event_constraint *
-intel_percore_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
+__intel_shared_reg_get_constraints(struct cpu_hw_events *cpuc,
+ struct hw_perf_event_extra *reg)
{
- struct hw_perf_event *hwc = &event->hw;
- unsigned int e = hwc->config & ARCH_PERFMON_EVENTSEL_EVENT;
- struct event_constraint *c;
- struct intel_percore *pc;
+ struct event_constraint *c = &emptyconstraint;
struct er_account *era;
- int i;
- int free_slot;
- int found;

- if (!x86_pmu.percore_constraints || hwc->extra_alloc)
- return NULL;
+ /* already allocated shared msr */
+ if (reg->alloc || !cpuc->shared_regs)
+ return &unconstrained;

- for (c = x86_pmu.percore_constraints; c->cmask; c++) {
- if (e != c->code)
- continue;
+ era = &cpuc->shared_regs->regs[reg->idx];
+
+ raw_spin_lock(&era->lock);
+
+ if (!atomic_read(&era->ref) || era->config == reg->config) {
+
+ /* lock in msr value */
+ era->config = reg->config;
+ era->reg = reg->reg;
+
+ /* one more user */
+ atomic_inc(&era->ref);
+
+ /* no need to reallocate during incremental event scheduling */
+ reg->alloc = 1;

/*
- * Allocate resource per core.
+ * All events using extra_reg are unconstrained.
+ * Avoids calling x86_get_event_constraints()
+ *
+ * Must revisit if extra_reg controlling events
+ * ever have constraints. Worst case we go through
+ * the regular event constraint table.
*/
- pc = cpuc->per_core;
- if (!pc)
- break;
- c = &emptyconstraint;
- raw_spin_lock(&pc->lock);
- free_slot = -1;
- found = 0;
- for (i = 0; i < MAX_EXTRA_REGS; i++) {
- era = &pc->regs[i];
- if (era->ref > 0 && hwc->extra_reg == era->extra_reg) {
- /* Allow sharing same config */
- if (hwc->extra_config == era->extra_config) {
- era->ref++;
- cpuc->percore_used = 1;
- hwc->extra_alloc = 1;
- c = NULL;
- }
- /* else conflict */
- found = 1;
- break;
- } else if (era->ref == 0 && free_slot == -1)
- free_slot = i;
- }
- if (!found && free_slot != -1) {
- era = &pc->regs[free_slot];
- era->ref = 1;
- era->extra_reg = hwc->extra_reg;
- era->extra_config = hwc->extra_config;
- cpuc->percore_used = 1;
- hwc->extra_alloc = 1;
- c = NULL;
- }
- raw_spin_unlock(&pc->lock);
- return c;
+ c = &unconstrained;
}
+ raw_spin_unlock(&era->lock);

- return NULL;
+ return c;
}

+static void
+__intel_shared_reg_put_constraints(struct cpu_hw_events *cpuc,
+ struct hw_perf_event_extra *reg)
+{
+ struct er_account *era;
+
+ /*
+ * only put constraint if extra reg was actually
+ * allocated. Also takes care of event which do
+ * not use an extra shared reg
+ */
+ if (!reg->alloc)
+ return;
+
+ era = &cpuc->shared_regs->regs[reg->idx];
+
+ /* one fewer user */
+ atomic_dec(&era->ref);
+
+ /* allocate again next time */
+ reg->alloc = 0;
+}
+
+static struct event_constraint *
+intel_shared_regs_constraints(struct cpu_hw_events *cpuc,
+ struct perf_event *event)
+{
+ struct event_constraint *c = NULL;
+ struct hw_perf_event_extra *xreg;
+
+ xreg = &event->hw.extra_reg;
+ if (xreg->idx != EXTRA_REG_NONE)
+ c = __intel_shared_reg_get_constraints(cpuc, xreg);
+ return c;
+ }
+
static struct event_constraint *
intel_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event)
{
@@ -1111,49 +1112,28 @@ intel_get_event_constraints(struct cpu_hw_events *cpuc, struct perf_event *event
if (c)
return c;

- c = intel_percore_constraints(cpuc, event);
+ c = intel_shared_regs_constraints(cpuc, event);
if (c)
return c;

return x86_get_event_constraints(cpuc, event);
}

-static void intel_put_event_constraints(struct cpu_hw_events *cpuc,
+static void
+intel_put_shared_regs_event_constraints(struct cpu_hw_events *cpuc,
struct perf_event *event)
{
- struct extra_reg *er;
- struct intel_percore *pc;
- struct er_account *era;
- struct hw_perf_event *hwc = &event->hw;
- int i, allref;
-
- if (!cpuc->percore_used)
- return;
+ struct hw_perf_event_extra *reg;

- for (er = x86_pmu.extra_regs; er->msr; er++) {
- if (er->event != (hwc->config & er->config_mask))
- continue;
+ reg = &event->hw.extra_reg;
+ if (reg->idx != EXTRA_REG_NONE)
+ __intel_shared_reg_put_constraints(cpuc, reg);
+}

- pc = cpuc->per_core;
- raw_spin_lock(&pc->lock);
- for (i = 0; i < MAX_EXTRA_REGS; i++) {
- era = &pc->regs[i];
- if (era->ref > 0 &&
- era->extra_config == hwc->extra_config &&
- era->extra_reg == er->msr) {
- era->ref--;
- hwc->extra_alloc = 0;
- break;
- }
- }
- allref = 0;
- for (i = 0; i < MAX_EXTRA_REGS; i++)
- allref += pc->regs[i].ref;
- if (allref == 0)
- cpuc->percore_used = 0;
- raw_spin_unlock(&pc->lock);
- break;
- }
+static void intel_put_event_constraints(struct cpu_hw_events *cpuc,
+ struct perf_event *event)
+{
+ intel_put_shared_regs_event_constraints(cpuc, event);
}

static int intel_pmu_hw_config(struct perf_event *event)
@@ -1231,20 +1211,36 @@ static __initconst const struct x86_pmu core_pmu = {
.event_constraints = intel_core_event_constraints,
};

+static struct intel_shared_regs *allocate_shared_regs(int cpu)
+{
+ struct intel_shared_regs *regs;
+ int i;
+
+ regs = kzalloc_node(sizeof(struct intel_shared_regs),
+ GFP_KERNEL, cpu_to_node(cpu));
+ if (regs) {
+ /*
+ * initialize the locks to keep lockdep happy
+ */
+ for (i = 0; i < EXTRA_REG_MAX; i++)
+ raw_spin_lock_init(&regs->regs[i].lock);
+
+ regs->core_id = -1;
+ }
+ return regs;
+}
+
static int intel_pmu_cpu_prepare(int cpu)
{
struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);

- if (!cpu_has_ht_siblings())
+ if (!x86_pmu.extra_regs)
return NOTIFY_OK;

- cpuc->per_core = kzalloc_node(sizeof(struct intel_percore),
- GFP_KERNEL, cpu_to_node(cpu));
- if (!cpuc->per_core)
+ cpuc->shared_regs = allocate_shared_regs(cpu);
+ if (!cpuc->shared_regs)
return NOTIFY_BAD;

- raw_spin_lock_init(&cpuc->per_core->lock);
- cpuc->per_core->core_id = -1;
return NOTIFY_OK;
}

@@ -1260,32 +1256,34 @@ static void intel_pmu_cpu_starting(int cpu)
*/
intel_pmu_lbr_reset();

- if (!cpu_has_ht_siblings())
+ if (!cpuc->shared_regs)
return;

for_each_cpu(i, topology_thread_cpumask(cpu)) {
- struct intel_percore *pc = per_cpu(cpu_hw_events, i).per_core;
+ struct intel_shared_regs *pc;

+ pc = per_cpu(cpu_hw_events, i).shared_regs;
if (pc && pc->core_id == core_id) {
- kfree(cpuc->per_core);
- cpuc->per_core = pc;
+ kfree(cpuc->shared_regs);
+ cpuc->shared_regs = pc;
break;
}
}

- cpuc->per_core->core_id = core_id;
- cpuc->per_core->refcnt++;
+ cpuc->shared_regs->core_id = core_id;
+ cpuc->shared_regs->refcnt++;
}

static void intel_pmu_cpu_dying(int cpu)
{
struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
- struct intel_percore *pc = cpuc->per_core;
+ struct intel_shared_regs *pc;

+ pc = cpuc->shared_regs;
if (pc) {
if (pc->core_id == -1 || --pc->refcnt == 0)
kfree(pc);
- cpuc->per_core = NULL;
+ cpuc->shared_regs = NULL;
}

fini_debug_store_on_cpu(cpu);
@@ -1436,7 +1434,6 @@ static __init int intel_pmu_init(void)

x86_pmu.event_constraints = intel_nehalem_event_constraints;
x86_pmu.pebs_constraints = intel_nehalem_pebs_event_constraints;
- x86_pmu.percore_constraints = intel_nehalem_percore_constraints;
x86_pmu.enable_all = intel_pmu_nhm_enable_all;
x86_pmu.extra_regs = intel_nehalem_extra_regs;

@@ -1481,7 +1478,6 @@ static __init int intel_pmu_init(void)
intel_pmu_lbr_init_nhm();

x86_pmu.event_constraints = intel_westmere_event_constraints;
- x86_pmu.percore_constraints = intel_westmere_percore_constraints;
x86_pmu.enable_all = intel_pmu_nhm_enable_all;
x86_pmu.pebs_constraints = intel_westmere_pebs_event_constraints;
x86_pmu.extra_regs = intel_westmere_extra_regs;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3412684..941f40d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -536,6 +536,16 @@ struct perf_branch_stack {

struct task_struct;

+/*
+ * extra PMU register associated with an event
+ */
+struct hw_perf_event_extra {
+ u64 config; /* register value */
+ unsigned int reg; /* register address or index */
+ int alloc; /* extra register already allocated */
+ int idx; /* index in shared_regs->regs[] */
+};
+
/**
* struct hw_perf_event - performance event hardware details:
*/
@@ -549,9 +559,7 @@ struct hw_perf_event {
unsigned long event_base;
int idx;
int last_cpu;
- unsigned int extra_reg;
- u64 extra_config;
- int extra_alloc;
+ struct hw_perf_event_extra extra_reg;
};
struct { /* software */
struct hrtimer hrtimer;

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