From 2471bdda00c7ca94a0e5ebbef7e68db8c92a705f Mon Sep 17 00:00:00 2001
From: Klaus Post <klauspost@gmail.com>
Date: Tue, 5 Jul 2022 11:02:30 -0700
Subject: [PATCH] fix: for DiskInfo call cache disk metrics (#15229)

Small uploads spend a significant amount of time (~5%) fetching disk info metrics. Also maps are allocated for each call.

Add a 100ms cache to disk metrics.
---
 cmd/xl-storage-disk-id-check.go | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/cmd/xl-storage-disk-id-check.go b/cmd/xl-storage-disk-id-check.go
index 5b56b7d63..9d07ad194 100644
--- a/cmd/xl-storage-disk-id-check.go
+++ b/cmd/xl-storage-disk-id-check.go
@@ -78,20 +78,28 @@ type xlStorageDiskIDCheck struct {
 	diskID       string
 	storage      *xlStorage
 	health       *diskHealthTracker
+	metricsCache timedValue
 }
 
 func (p *xlStorageDiskIDCheck) getMetrics() DiskMetrics {
-	diskMetric := DiskMetrics{
-		APILatencies: make(map[string]uint64),
-		APICalls:     make(map[string]uint64),
-	}
-	for i, v := range p.apiLatencies {
-		diskMetric.APILatencies[storageMetric(i).String()] = v.value()
-	}
-	for i := range p.apiCalls {
-		diskMetric.APICalls[storageMetric(i).String()] = atomic.LoadUint64(&p.apiCalls[i])
-	}
-	return diskMetric
+	p.metricsCache.Once.Do(func() {
+		p.metricsCache.TTL = 100 * time.Millisecond
+		p.metricsCache.Update = func() (interface{}, error) {
+			diskMetric := DiskMetrics{
+				APILatencies: make(map[string]uint64, len(p.apiLatencies)),
+				APICalls:     make(map[string]uint64, len(p.apiCalls)),
+			}
+			for i, v := range p.apiLatencies {
+				diskMetric.APILatencies[storageMetric(i).String()] = v.value()
+			}
+			for i := range p.apiCalls {
+				diskMetric.APICalls[storageMetric(i).String()] = atomic.LoadUint64(&p.apiCalls[i])
+			}
+			return diskMetric, nil
+		}
+	})
+	m, _ := p.metricsCache.Get()
+	return m.(DiskMetrics)
 }
 
 type lockedLastMinuteLatency struct {