Internal change.

PiperOrigin-RevId: 235053594
Change-Id: Ie3d7b11843d0710184a2463886c7034e8f5305d1

1 files changed, 29 insertions, 1 deletions

diff --git a/pkg/sentry/fs/file.go b/pkg/sentry/fs/file.go
index b66d2f265..d66813103 100644
--- a/pkg/sentry/fs/file.go
+++ b/pkg/sentry/fs/file.go
@@ -18,6 +18,7 @@ import (
 	"math"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"gvisor.googlesource.com/gvisor/pkg/amutex"
 	"gvisor.googlesource.com/gvisor/pkg/log"
@@ -33,7 +34,22 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
 )
 
-var reads = metric.MustCreateNewUint64Metric("/fs/reads", false /* sync */, "Number of file reads.")
+var (
+	// RecordWaitTime controls writing metrics for filesystem reads. Enabling this comes at a small
+	// CPU cost due to performing two monotonic clock reads per read call.
+	RecordWaitTime = false
+
+	reads    = metric.MustCreateNewUint64Metric("/fs/reads", false /* sync */, "Number of file reads.")
+	readWait = metric.MustCreateNewUint64Metric("/fs/read_wait", false /* sync */, "Time waiting on file reads, in nanoseconds.")
+)
+
+// IncrementWait increments the given wait time metric, if enabled.
+func IncrementWait(m *metric.Uint64Metric, start time.Time) {
+	if !RecordWaitTime {
+		return
+	}
+	m.IncrementBy(uint64(time.Since(start)))
+}
 
 // FileMaxOffset is the maximum possible file offset.
 const FileMaxOffset = math.MaxInt64
@@ -236,7 +252,12 @@ func (f *File) Readdir(ctx context.Context, serializer DentrySerializer) error {
 //
 // Returns syserror.ErrInterrupted if reading was interrupted.
 func (f *File) Readv(ctx context.Context, dst usermem.IOSequence) (int64, error) {
+	var start time.Time
+	if RecordWaitTime {
+		start = time.Now()
+	}
 	if !f.mu.Lock(ctx) {
+		IncrementWait(readWait, start)
 		return 0, syserror.ErrInterrupted
 	}
 
@@ -246,6 +267,7 @@ func (f *File) Readv(ctx context.Context, dst usermem.IOSequence) (int64, error)
 		atomic.AddInt64(&f.offset, n)
 	}
 	f.mu.Unlock()
+	IncrementWait(readWait, start)
 	return n, err
 }
 
@@ -255,13 +277,19 @@ func (f *File) Readv(ctx context.Context, dst usermem.IOSequence) (int64, error)
 //
 // Otherwise same as Readv.
 func (f *File) Preadv(ctx context.Context, dst usermem.IOSequence, offset int64) (int64, error) {
+	var start time.Time
+	if RecordWaitTime {
+		start = time.Now()
+	}
 	if !f.mu.Lock(ctx) {
+		IncrementWait(readWait, start)
 		return 0, syserror.ErrInterrupted
 	}
 
 	reads.Increment()
 	n, err := f.FileOperations.Read(ctx, f, dst, offset)
 	f.mu.Unlock()
+	IncrementWait(readWait, start)
 	return n, err
 }