linux-kernel - [PATCH 2/3] perf/x86/mbm: Store bytes counted for mbm during recycle

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Message-Id: <1461776456-25246-3-git-send-email-vikas.shivappa@linux.intel.com>
Date:	Wed, 27 Apr 2016 10:00:55 -0700
From:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
To:	vikas.shivappa@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de
Cc:	mingo@...nel.org, peterz@...radead.org, ravi.v.shankar@...el.com,
	tony.luck@...el.com, fenghua.yu@...el.com,
	vikas.shivappa@...ux.intel.com
Subject: [PATCH 2/3] perf/x86/mbm: Store bytes counted for mbm during recycle

For MBM, since we report total bytes for the duration the perf counts,
we need to keep the total bytes counted every time we loose an RMID.
Introduce rc_count(recycle count) per event
keep this history count(all bytes counted before the current RMID).

If we do not keep this count separately then we may end up sending a
count that may be less than the previous count during -I perf stat
option which leads to negative numbers being reported in the perf. This
happens say when we counted a greater amount with RMID1 and then
counted lesser with RMID2, and if user checks counts in interval mode
after RMID1 and then again after RMID2.

Signed-off-by: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
---
 arch/x86/events/intel/cqm.c | 49 ++++++++++++++++++++++++++++++++++++++++-----
 include/linux/perf_event.h  |  1 +
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/intel/cqm.c b/arch/x86/events/intel/cqm.c
index 5f2104a..320af26 100644
--- a/arch/x86/events/intel/cqm.c
+++ b/arch/x86/events/intel/cqm.c
@@ -479,6 +479,16 @@ static void cqm_mask_call(struct rmid_read *rr)
 		on_each_cpu_mask(&cqm_cpumask, __intel_cqm_event_count, rr, 1);
 }
 
+static inline void
+mbm_set_rccount(struct perf_event *event, struct rmid_read *rr)
+{
+	u64 tmpval;
+
+	tmpval = local64_read(&event->hw.rc_count) + atomic64_read(&rr->value);
+	local64_set(&event->hw.rc_count, tmpval);
+	local64_set(&event->count, tmpval);
+}
+
 /*
  * Exchange the RMID of a group of events.
  */
@@ -493,12 +503,19 @@ static u32 intel_cqm_xchg_rmid(struct perf_event *group, u32 rmid)
 
 	/*
 	 * If our RMID is being deallocated, perform a read now.
+	 * For mbm, we need to store the bytes that were counted till now
+	 * separately.
 	 */
 	if (__rmid_valid(old_rmid) && !__rmid_valid(rmid)) {
 
 		rr = __init_rr(old_rmid, group->attr.config, 0);
 		cqm_mask_call(&rr);
-		local64_set(&group->count, atomic64_read(&rr.value));
+
+		if (is_mbm_event(group->attr.config))
+			mbm_set_rccount(group, &rr);
+		else
+			local64_set(&group->count, atomic64_read(&rr.value));
+
 		list_for_each_entry(event, head, hw.cqm_group_entry) {
 			if (event->hw.is_group_event) {
 
@@ -506,8 +523,11 @@ static u32 intel_cqm_xchg_rmid(struct perf_event *group, u32 rmid)
 				rr = __init_rr(old_rmid, evttype, 0);
 
 				cqm_mask_call(&rr);
-				local64_set(&event->count,
-					    atomic64_read(&rr.value));
+				if (is_mbm_event(event->attr.config))
+					mbm_set_rccount(event, &rr);
+				else
+					local64_set(&event->count,
+						    atomic64_read(&rr.value));
 			}
 		}
 	}
@@ -1194,6 +1214,7 @@ static u64 intel_cqm_event_count(struct perf_event *event)
 {
 	unsigned long flags;
 	struct rmid_read rr = __init_rr(-1, event->attr.config, 0);
+	u64 tmpval;
 
 	/*
 	 * We only need to worry about task events. System-wide events
@@ -1235,6 +1256,16 @@ static u64 intel_cqm_event_count(struct perf_event *event)
 	 * busying performing the IPI calls. It's therefore necessary to
 	 * check @event's RMID afterwards, and if it has changed,
 	 * discard the result of the read.
+	 *
+	 * For MBM events, we are reading the total bytes and not
+	 * a snapshot. Hence if RMIDs were recycled for the event, we need
+	 * to add the counts of all RMIDs associated with the event together.
+	 * Suppose RMID(1).. RMID(k) represent the total_bytes of the
+	 * different RMIDs the event was associated with,
+	 * count = RMID(1) + RMID(2) +...+ RMID(k-1)+ RMID(k).
+	 *       = rc_count + RMID(k).
+	 * RMID(k) - is the count we read now via IPI
+	 * rc_count = RMID(1) + RMID(2) +...+ RMID(k-1).
 	 */
 	rr.rmid = ACCESS_ONCE(event->hw.cqm_rmid);
 
@@ -1244,8 +1275,16 @@ static u64 intel_cqm_event_count(struct perf_event *event)
 	cqm_mask_call(&rr);
 
 	raw_spin_lock_irqsave(&cache_lock, flags);
-	if (event->hw.cqm_rmid == rr.rmid)
-		local64_set(&event->count, atomic64_read(&rr.value));
+	if (event->hw.cqm_rmid == rr.rmid) {
+		if (is_mbm_event(event->attr.config)) {
+			tmpval = atomic64_read(&rr.value) +
+				local64_read(&event->hw.rc_count);
+
+			local64_set(&event->count, tmpval);
+		} else {
+			local64_set(&event->count, atomic64_read(&rr.value));
+		}
+	}
 	raw_spin_unlock_irqrestore(&cache_lock, flags);
 out:
 	return __perf_event_count(event);
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index f291275..ec7772a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -122,6 +122,7 @@ struct hw_perf_event {
 			int			cqm_state;
 			u32			cqm_rmid;
 			int			is_group_event;
+			local64_t		rc_count;
 			struct list_head	cqm_events_entry;
 			struct list_head	cqm_groups_entry;
 			struct list_head	cqm_group_entry;
-- 
1.9.1