This patch provides basic enablement for perf branch stack sampling framework
on POWER8 processor with a new PMU feature called BHRB (Branch History Rolling
Buffer).
Signed-off-by: Anshuman Khandual <khand...@linux.vnet.ibm.com>
---
arch/powerpc/perf/core-book3s.c | 96 +++++++++++++++++++++++++++++++++++--
arch/powerpc/perf/perf_event_bhrb.c | 75 +++++++++++++++++++++++++++++
2 files changed, 168 insertions(+), 3 deletions(-)
create mode 100644 arch/powerpc/perf/perf_event_bhrb.c
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 4ac6e64..f4d1347 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -19,6 +19,8 @@
#include <asm/firmware.h>
#include <asm/ptrace.h>
+#define BHRB_MAX_ENTRIES 32
+
struct cpu_hw_events {
int n_events;
int n_percpu;
@@ -38,11 +40,21 @@ struct cpu_hw_events {
unsigned int group_flag;
int n_txn_start;
+
+ /* BHRB bits */
+ u64 bhrb_filter; /* BHRB HW branch
filter */
+ int bhrb_users;
+ void *bhrb_context;
+ struct perf_branch_stack bhrb_stack;
+ struct perf_branch_entry bhrb_entries[BHRB_MAX_ENTRIES];
};
+
DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events);
struct power_pmu *ppmu;
+#include "perf_event_bhrb.c"
+
/*
* Normally, to ignore kernel events we set the FCS (freeze counters
* in supervisor mode) bit in MMCR0, but if the kernel runs with the
@@ -858,6 +870,9 @@ static void power_pmu_enable(struct pmu *pmu)
}
out:
+ if (cpuhw->bhrb_users)
+ ppmu->config_bhrb(cpuhw->bhrb_filter);
+
local_irq_restore(flags);
}
@@ -888,6 +903,47 @@ static int collect_events(struct perf_event *group, int
max_count,
return n;
}
+/* Reset all possible BHRB entries */
+static void power_pmu_bhrb_reset(void)
+{
+ asm volatile(PPC_CLRBHRB);
+}
+
+void power_pmu_bhrb_enable(struct perf_event *event)
+{
+ struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
+
+ if (!ppmu->bhrb_nr)
+ return;
+
+ /* Clear BHRB if we changed task context to avoid data leaks */
+ if (event->ctx->task && cpuhw->bhrb_context != event->ctx) {
+ power_pmu_bhrb_reset();
+ cpuhw->bhrb_context = event->ctx;
+ }
+ cpuhw->bhrb_users++;
+}
+
+void power_pmu_bhrb_disable(struct perf_event *event)
+{
+ struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
+
+ if (!ppmu->bhrb_nr)
+ return;
+
+ cpuhw->bhrb_users--;
+ WARN_ON_ONCE(cpuhw->bhrb_users < 0);
+
+ if (!cpuhw->disabled && !cpuhw->bhrb_users) {
+ /* BHRB cannot be turned off when other
+ * events are active on the PMU.
+ */
+
+ /* avoid stale pointer */
+ cpuhw->bhrb_context = NULL;
+ }
+}
+
/*
* Add a event to the PMU.
* If all events are not already frozen, then we disable and
@@ -947,6 +1003,9 @@ nocheck:
ret = 0;
out:
+ if (has_branch_stack(event))
+ power_pmu_bhrb_enable(event);
+
perf_pmu_enable(event->pmu);
local_irq_restore(flags);
return ret;
@@ -999,6 +1058,9 @@ static void power_pmu_del(struct perf_event *event, int
ef_flags)
cpuhw->mmcr[0] &= ~(MMCR0_PMXE | MMCR0_FCECE);
}
+ if (has_branch_stack(event))
+ power_pmu_bhrb_disable(event);
+
perf_pmu_enable(event->pmu);
local_irq_restore(flags);
}
@@ -1117,6 +1179,15 @@ int power_pmu_commit_txn(struct pmu *pmu)
return 0;
}
+/* Called from ctxsw to prevent one process's branch entries to
+ * mingle with the other process's entries during context switch.
+ */
+void power_pmu_flush_branch_stack(void)
+{
+ if (ppmu->bhrb_nr)
+ power_pmu_bhrb_reset();
+}
+
/*
* Return 1 if we might be able to put event on a limited PMC,
* or 0 if not.
@@ -1231,9 +1302,11 @@ static int power_pmu_event_init(struct perf_event *event)
if (!ppmu)
return -ENOENT;
- /* does not support taken branch sampling */
- if (has_branch_stack(event))
- return -EOPNOTSUPP;
+ if (has_branch_stack(event)) {
+ /* PMU has BHRB enabled */
+ if (!(ppmu->flags & PPMU_BHRB))
+ return -EOPNOTSUPP;
+ }
switch (event->attr.type) {
case PERF_TYPE_HARDWARE:
@@ -1314,6 +1387,15 @@ static int power_pmu_event_init(struct perf_event *event)
cpuhw = &get_cpu_var(cpu_hw_events);
err = power_check_constraints(cpuhw, events, cflags, n + 1);
+
+ if (has_branch_stack(event)) {
+ cpuhw->bhrb_filter = ppmu->bhrb_filter_map(
+ event->attr.branch_sample_type);
+
+ if(cpuhw->bhrb_filter == -1)
+ return -EOPNOTSUPP;
+ }
+
put_cpu_var(cpu_hw_events);
if (err)
return -EINVAL;
@@ -1372,6 +1454,7 @@ struct pmu power_pmu = {
.cancel_txn = power_pmu_cancel_txn,
.commit_txn = power_pmu_commit_txn,
.event_idx = power_pmu_event_idx,
+ .flush_branch_stack = power_pmu_flush_branch_stack,
};
@@ -1433,6 +1516,13 @@ static void record_and_restart(struct perf_event *event,
unsigned long val,
if (event->attr.sample_type & PERF_SAMPLE_ADDR)
perf_get_data_addr(regs, &data.addr);
+ if (event->attr.sample_type & PERF_SAMPLE_BRANCH_STACK) {
+ struct cpu_hw_events *cpuhw;
+ cpuhw = &__get_cpu_var(cpu_hw_events);
+ power_pmu_bhrb_read(cpuhw);
+ data.br_stack = &cpuhw->bhrb_stack;
+ }
+
if (perf_event_overflow(event, &data, regs))
power_pmu_stop(event, 0);
}
diff --git a/arch/powerpc/perf/perf_event_bhrb.c
b/arch/powerpc/perf/perf_event_bhrb.c
new file mode 100644
index 0000000..5beddef
--- /dev/null
+++ b/arch/powerpc/perf/perf_event_bhrb.c
@@ -0,0 +1,75 @@
+#define BHRB_TARGET 0x0000000000000002
+#define BHRB_PREDICTION 0x0000000000000001
+#define BHRB_EA 0xFFFFFFFFFFFFFFFC
+
+extern unsigned long int read_bhrb(int n);
+
+void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
+{
+ u64 val;
+ u64 addr;
+ int r_index, u_index, target, pred;
+
+ r_index = 0;
+ u_index = 0;
+ while (r_index < ppmu->bhrb_nr) {
+ /* Assembly read function */
+ val = read_bhrb(r_index);
+
+ /* Terminal marker: End of valid BHRB entries */
+ if (val == 0) {
+ break;
+ } else {
+ /* BHRB field break up */
+ addr = val & BHRB_EA;
+ pred = val & BHRB_PREDICTION;
+ target = val & BHRB_TARGET;
+
+ /* Probable Missed entry: Not applicable for POWER8 */
+ if ((addr == 0) && (target == 0) && (pred == 1)) {
+ r_index++;
+ continue;
+ }
+
+ /* Real Missed entry: Power8 based missed entry */
+ if ((addr == 0) && (target == 1) && (pred == 1)) {
+ r_index++;
+ continue;
+ }
+
+ /* Reserved condition: Not a valid entry */
+ if ((addr == 0) && (target == 1) && (pred == 0)) {
+ r_index++;
+ continue;
+ }
+
+ /* Is a target address */
+ if (val & BHRB_TARGET) {
+ /* First address cannot be a target address */
+ if (r_index == 0) {
+ r_index++;
+ continue;
+ }
+
+ /* Update target address for the previous entry
*/
+ cpuhw->bhrb_entries[u_index - 1].to = addr;
+ cpuhw->bhrb_entries[u_index - 1].mispred = pred;
+ cpuhw->bhrb_entries[u_index - 1].predicted =
~pred;
+
+ /* Dont increment u_index */
+ r_index++;
+ } else {
+ /* Update address, flags for current entry */
+ cpuhw->bhrb_entries[u_index].from = addr;
+ cpuhw->bhrb_entries[u_index].mispred = pred;
+ cpuhw->bhrb_entries[u_index].predicted = ~pred;
+
+ /* Successfully popullated one entry */
+ u_index++;
+ r_index++;
+ }
+ }
+ }
+ cpuhw->bhrb_stack.nr = u_index;
+ return;
+}
--
1.7.11.7
--
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