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Subject[PATCH 06/12] perf_events: implement PERF_SAMPLE_BRANCH for Intel X86
Date
This patch implements PERF_SAMPLE_BRANCH support for Intel
X86 processors. It connects PERF_SAMPLE_BRANCH to the actual LBR.

The patch adds the hooks in the PMU irq handler to save the LBR
on counter overflow for both regular and PEBS modes.

Signed-off-by: Stephane Eranian <eranian@google.com>
---
arch/x86/kernel/cpu/perf_event_intel.c | 35 +++++++++++++
arch/x86/kernel/cpu/perf_event_intel_ds.c | 10 ++--
arch/x86/kernel/cpu/perf_event_intel_lbr.c | 73 +++++++++++++++++++++++++++-
include/linux/perf_event.h | 3 +
4 files changed, 113 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 740857f..b5e7c52 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -727,6 +727,19 @@ static __initconst const u64 atom_hw_cache_event_ids
},
};

+static inline bool intel_pmu_needs_lbr_smpl(struct perf_event *event)
+{
+ /* user explicitly requested branch sampling */
+ if (has_branch_stack(event))
+ return true;
+
+ /* implicit branch sampling to correct PEBS skid */
+ if (x86_pmu.intel_cap.pebs_trap && event->attr.precise_ip > 1)
+ return true;
+
+ return false;
+}
+
static void intel_pmu_disable_all(void)
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
@@ -876,6 +889,13 @@ static void intel_pmu_disable_event(struct perf_event *event)
return;
}

+ /*
+ * must disable before any actual event
+ * because any event may be combined with LBR
+ */
+ if (intel_pmu_needs_lbr_smpl(event))
+ intel_pmu_lbr_disable(event);
+
if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL)) {
intel_pmu_disable_fixed(hwc);
return;
@@ -929,6 +949,12 @@ static void intel_pmu_enable_event(struct perf_event *event)
intel_pmu_enable_bts(hwc->config);
return;
}
+ /*
+ * must enabled before any actual event
+ * because any event may be combined with LBR
+ */
+ if (intel_pmu_needs_lbr_smpl(event))
+ intel_pmu_lbr_enable(event);

if (unlikely(hwc->config_base == MSR_ARCH_PERFMON_FIXED_CTR_CTRL)) {
intel_pmu_enable_fixed(hwc);
@@ -1046,6 +1072,9 @@ again:

data.period = event->hw.last_period;

+ if (has_branch_stack(event))
+ data.br_stack = &cpuc->lbr_stack;
+
if (perf_event_overflow(event, &data, regs))
x86_pmu_stop(event, 0);
}
@@ -1279,6 +1308,12 @@ static int intel_pmu_hw_config(struct perf_event *event)
event->hw.config = alt_config;
}

+ if (intel_pmu_needs_lbr_smpl(event)) {
+ ret = intel_pmu_setup_lbr_filter(event);
+ if (ret)
+ return ret;
+ }
+
if (event->attr.type != PERF_TYPE_RAW)
return 0;

diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index 1b1ef3a..238d82f 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -455,9 +455,6 @@ static void intel_pmu_pebs_enable(struct perf_event *event)

cpuc->pebs_enabled |= 1ULL << hwc->idx;
WARN_ON_ONCE(cpuc->enabled);
-
- if (x86_pmu.intel_cap.pebs_trap && event->attr.precise_ip > 1)
- intel_pmu_lbr_enable(event);
}

static void intel_pmu_pebs_disable(struct perf_event *event)
@@ -470,9 +467,6 @@ static void intel_pmu_pebs_disable(struct perf_event *event)
wrmsrl(MSR_IA32_PEBS_ENABLE, cpuc->pebs_enabled);

hwc->config |= ARCH_PERFMON_EVENTSEL_INT;
-
- if (x86_pmu.intel_cap.pebs_trap && event->attr.precise_ip > 1)
- intel_pmu_lbr_disable(event);
}

static void intel_pmu_pebs_enable_all(void)
@@ -586,6 +580,7 @@ static void __intel_pmu_pebs_event(struct perf_event *event,
* both formats and we don't use the other fields in this
* routine.
*/
+ struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
struct pebs_record_core *pebs = __pebs;
struct perf_sample_data data;
struct pt_regs regs;
@@ -616,6 +611,9 @@ static void __intel_pmu_pebs_event(struct perf_event *event,
else
regs.flags &= ~PERF_EFLAGS_EXACT;

+ if (has_branch_stack(event))
+ data.br_stack = &cpuc->lbr_stack;
+
if (perf_event_overflow(event, &data, &regs))
x86_pmu_stop(event, 0);
}
diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index abcabe3..76c4639 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -36,6 +36,7 @@ enum {
#define LBR_PLM (LBR_KERNEL | LBR_USER)

#define LBR_SEL_MASK 0x1ff /* valid bits in LBR_SELECT */
+#define LBR_NOT_SUPP -1 /* LBR filter not supported */

#define LBR_ANY \
(LBR_JCC |\
@@ -48,6 +49,10 @@ enum {

#define LBR_FROM_FLAG_MISPRED (1ULL << 63)

+#define for_each_branch_sample_type(x) \
+ for ((x) = PERF_SAMPLE_BRANCH_USER; \
+ (x) < PERF_SAMPLE_BRANCH_MAX; (x) <<= 1)
+
/*
* We only support LBR implementations that have FREEZE_LBRS_ON_PMI
* otherwise it becomes near impossible to get a reliable stack.
@@ -56,6 +61,10 @@ enum {
static void __intel_pmu_lbr_enable(void)
{
u64 debugctl;
+ struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
+
+ if (cpuc->lbr_sel)
+ wrmsrl(MSR_LBR_SELECT, cpuc->lbr_sel->config);

rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
debugctl |= (DEBUGCTLMSR_LBR | DEBUGCTLMSR_FREEZE_LBRS_ON_PMI);
@@ -113,7 +122,6 @@ static void intel_pmu_lbr_enable(struct perf_event *event)
* Reset the LBR stack if we changed task context to
* avoid data leaks.
*/
-
if (event->ctx->task && cpuc->lbr_context != event->ctx) {
intel_pmu_lbr_reset();
cpuc->lbr_context = event->ctx;
@@ -132,8 +140,11 @@ static void intel_pmu_lbr_disable(struct perf_event *event)
cpuc->lbr_users--;
WARN_ON_ONCE(cpuc->lbr_users < 0);

- if (cpuc->enabled && !cpuc->lbr_users)
+ if (cpuc->enabled && !cpuc->lbr_users) {
__intel_pmu_lbr_disable();
+ /* avoid stale pointer */
+ cpuc->lbr_context = NULL;
+ }
}

static void intel_pmu_lbr_enable_all(void)
@@ -152,6 +163,9 @@ static void intel_pmu_lbr_disable_all(void)
__intel_pmu_lbr_disable();
}

+/*
+ * TOS = most recently recorded branch
+ */
static inline u64 intel_pmu_lbr_tos(void)
{
u64 tos;
@@ -236,6 +250,61 @@ static void intel_pmu_lbr_read(void)
}

/*
+ * setup the HW LBR filter
+ * Used only when available, may not be enough to disambiguate
+ * all branches, may need the help of the SW filter
+ */
+static int intel_pmu_setup_hw_lbr_filter(struct perf_event *event)
+{
+ struct hw_perf_event_extra *reg;
+ u64 br_type = event->attr.branch_sample_type;
+ u64 mask = 0, m;
+ u64 v;
+
+ for_each_branch_sample_type(m) {
+ if (!(br_type & m))
+ continue;
+
+ v = x86_pmu.lbr_sel_map[m];
+ if (v == LBR_NOT_SUPP)
+ return -EOPNOTSUPP;
+ mask |= v;
+
+ if (m == PERF_SAMPLE_BRANCH_ANY)
+ break;
+ }
+ reg = &event->hw.branch_reg;
+ reg->idx = EXTRA_REG_LBR;
+
+ /* LBR_SELECT operates in suppress mode so invert mask */
+ reg->config = ~mask & x86_pmu.lbr_sel_mask;
+
+ return 0;
+}
+
+static int intel_pmu_setup_lbr_filter(struct perf_event *event)
+{
+ u64 br_type = event->attr.branch_sample_type;
+
+ /*
+ * no LBR on this PMU
+ */
+ if (!x86_pmu.lbr_nr)
+ return -EOPNOTSUPP;
+
+ /*
+ * if no LBR HW filter, users can only
+ * capture all branches
+ */
+ if (!x86_pmu.lbr_sel_map) {
+ if (br_type != PERF_SAMPLE_BRANCH_ALL)
+ return -EOPNOTSUPP;
+ return 0;
+ }
+ return intel_pmu_setup_hw_lbr_filter(event);
+}
+
+/*
* Map interface branch filters onto LBR filters
*/
static const int nhm_lbr_sel_map[PERF_SAMPLE_BRANCH_MAX]=
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 850bbbe..0819364 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -159,6 +159,9 @@ enum perf_branch_sample_type {
(PERF_SAMPLE_BRANCH_USER|\
PERF_SAMPLE_BRANCH_KERNEL)

+#define PERF_SAMPLE_BRANCH_ALL \
+ (PERF_SAMPLE_BRANCH_PLM_ALL|PERF_SAMPLE_BRANCH_ANY)
+
/*
* The format of the data returned by read() on a perf event fd,
* as specified by attr.read_format:
--
1.7.4.1


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