perf/x86/intel: Support branch counters logging

The branch counters logging (A.K.A LBR event logging) introduces a
per-counter indication of precise event occurrences in LBRs. It can
provide a means to attribute exposed retirement latency to combinations
of events across a block of instructions. It also provides a means of
attributing Timed LBR latencies to events.

The feature is first introduced on SRF/GRR. It is an enhancement of the
ARCH LBR. It adds new fields in the LBR_INFO MSRs to log the occurrences
of events on the GP counters. The information is displayed by the order
of counters.

The design proposed in this patch requires that the events which are
logged must be in a group with the event that has LBR. If there are
more than one LBR group, the counters logging information only from the
current group (overflowed) are stored for the perf tool, otherwise the
perf tool cannot know which and when other groups are scheduled
especially when multiplexing is triggered. The user can ensure it uses
the maximum number of counters that support LBR info (4 by now) by
making the group large enough.

The HW only logs events by the order of counters. The order may be
different from the order of enabling which the perf tool can understand.
When parsing the information of each branch entry, convert the counter
order to the enabled order, and store the enabled order in the extension
space.

Unconditionally reset LBRs for an LBR event group when it's deleted. The
logged counter information is only valid for the current LBR group. If
another LBR group is scheduled later, the information from the stale
LBRs would be otherwise wrongly interpreted.

Add a sanity check in intel_pmu_hw_config(). Disable the feature if other
counter filters (inv, cmask, edge, in_tx) are set or LBR call stack mode
is enabled. (For the LBR call stack mode, we cannot simply flush the
LBR, since it will break the call stack. Also, there is no obvious usage
with the call stack mode for now.)

Only applying the PERF_SAMPLE_BRANCH_COUNTERS doesn't require any branch
stack setup.

Expose the maximum number of supported counters and the width of the
counters into the sysfs. The perf tool can use the information to parse
the logged counters in each branch.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20231025201626.3000228-5-kan.liang@linux.intel.com

1 files changed, 84 insertions, 1 deletions

diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index c3b0d15a9841..78cd5084104e 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -676,6 +676,25 @@ void intel_pmu_lbr_del(struct perf_event *event)
 	WARN_ON_ONCE(cpuc->lbr_users < 0);
 	WARN_ON_ONCE(cpuc->lbr_pebs_users < 0);
 	perf_sched_cb_dec(event->pmu);
+
+	/*
+	 * The logged occurrences information is only valid for the
+	 * current LBR group. If another LBR group is scheduled in
+	 * later, the information from the stale LBRs will be wrongly
+	 * interpreted. Reset the LBRs here.
+	 *
+	 * Only clear once for a branch counter group with the leader
+	 * event. Because
+	 * - Cannot simply reset the LBRs with the !cpuc->lbr_users.
+	 *   Because it's possible that the last LBR user is not in a
+	 *   branch counter group, e.g., a branch_counters group +
+	 *   several normal LBR events.
+	 * - The LBR reset can be done with any one of the events in a
+	 *   branch counter group, since they are always scheduled together.
+	 *   It's easy to force the leader event an LBR event.
+	 */
+	if (is_branch_counters_group(event) && event == event->group_leader)
+		intel_pmu_lbr_reset();
 }
 
 static inline bool vlbr_exclude_host(void)
@@ -866,6 +885,8 @@ static __always_inline u16 get_lbr_cycles(u64 info)
 	return cycles;
 }
 
+static_assert((64 - PERF_BRANCH_ENTRY_INFO_BITS_MAX) > LBR_INFO_BR_CNTR_NUM * LBR_INFO_BR_CNTR_BITS);
+
 static void intel_pmu_store_lbr(struct cpu_hw_events *cpuc,
 				struct lbr_entry *entries)
 {
@@ -898,11 +919,67 @@ static void intel_pmu_store_lbr(struct cpu_hw_events *cpuc,
 		e->abort	= !!(info & LBR_INFO_ABORT);
 		e->cycles	= get_lbr_cycles(info);
 		e->type		= get_lbr_br_type(info);
+
+		/*
+		 * Leverage the reserved field of cpuc->lbr_entries[i] to
+		 * temporarily store the branch counters information.
+		 * The later code will decide what content can be disclosed
+		 * to the perf tool. Pleae see intel_pmu_lbr_counters_reorder().
+		 */
+		e->reserved	= (info >> LBR_INFO_BR_CNTR_OFFSET) & LBR_INFO_BR_CNTR_FULL_MASK;
 	}
 
 	cpuc->lbr_stack.nr = i;
 }
 
+/*
+ * The enabled order may be different from the counter order.
+ * Update the lbr_counters with the enabled order.
+ */
+static void intel_pmu_lbr_counters_reorder(struct cpu_hw_events *cpuc,
+					   struct perf_event *event)
+{
+	int i, j, pos = 0, order[X86_PMC_IDX_MAX];
+	struct perf_event *leader, *sibling;
+	u64 src, dst, cnt;
+
+	leader = event->group_leader;
+	if (branch_sample_counters(leader))
+		order[pos++] = leader->hw.idx;
+
+	for_each_sibling_event(sibling, leader) {
+		if (!branch_sample_counters(sibling))
+			continue;
+		order[pos++] = sibling->hw.idx;
+	}
+
+	WARN_ON_ONCE(!pos);
+
+	for (i = 0; i < cpuc->lbr_stack.nr; i++) {
+		src = cpuc->lbr_entries[i].reserved;
+		dst = 0;
+		for (j = 0; j < pos; j++) {
+			cnt = (src >> (order[j] * LBR_INFO_BR_CNTR_BITS)) & LBR_INFO_BR_CNTR_MASK;
+			dst |= cnt << j * LBR_INFO_BR_CNTR_BITS;
+		}
+		cpuc->lbr_counters[i] = dst;
+		cpuc->lbr_entries[i].reserved = 0;
+	}
+}
+
+void intel_pmu_lbr_save_brstack(struct perf_sample_data *data,
+				struct cpu_hw_events *cpuc,
+				struct perf_event *event)
+{
+	if (is_branch_counters_group(event)) {
+		intel_pmu_lbr_counters_reorder(cpuc, event);
+		perf_sample_save_brstack(data, event, &cpuc->lbr_stack, cpuc->lbr_counters);
+		return;
+	}
+
+	perf_sample_save_brstack(data, event, &cpuc->lbr_stack, NULL);
+}
+
 static void intel_pmu_arch_lbr_read(struct cpu_hw_events *cpuc)
 {
 	intel_pmu_store_lbr(cpuc, NULL);
@@ -1173,8 +1250,10 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
 	for (i = 0; i < cpuc->lbr_stack.nr; ) {
 		if (!cpuc->lbr_entries[i].from) {
 			j = i;
-			while (++j < cpuc->lbr_stack.nr)
+			while (++j < cpuc->lbr_stack.nr) {
 				cpuc->lbr_entries[j-1] = cpuc->lbr_entries[j];
+				cpuc->lbr_counters[j-1] = cpuc->lbr_counters[j];
+			}
 			cpuc->lbr_stack.nr--;
 			if (!cpuc->lbr_entries[i].from)
 				continue;
@@ -1525,8 +1604,12 @@ void __init intel_pmu_arch_lbr_init(void)
 	x86_pmu.lbr_mispred = ecx.split.lbr_mispred;
 	x86_pmu.lbr_timed_lbr = ecx.split.lbr_timed_lbr;
 	x86_pmu.lbr_br_type = ecx.split.lbr_br_type;
+	x86_pmu.lbr_counters = ecx.split.lbr_counters;
 	x86_pmu.lbr_nr = lbr_nr;
 
+	if (!!x86_pmu.lbr_counters)
+		x86_pmu.flags |= PMU_FL_BR_CNTR;
+
 	if (x86_pmu.lbr_mispred)
 		static_branch_enable(&x86_lbr_mispred);
 	if (x86_pmu.lbr_timed_lbr)