Check thread group CPU timers in the CPU clock ticker.

This reduces the number of goroutines and runtime timers when
ITIMER_VIRTUAL or ITIMER_PROF are enabled, or when RLIMIT_CPU is set.
This also ensures that thread group CPU timers only advance if running
tasks are observed at the time the CPU clock advances, mostly
eliminating the possibility that a CPU timer expiration observes no
running tasks and falls back to the group leader.

PiperOrigin-RevId: 217603396
Change-Id: Ia24ce934d5574334857d9afb5ad8ca0b6a6e65f4

1 files changed, 26 insertions, 0 deletions

diff --git a/pkg/sentry/kernel/timekeeper.go b/pkg/sentry/kernel/timekeeper.go
index df5dbe128..2167f3efe 100644
--- a/pkg/sentry/kernel/timekeeper.go
+++ b/pkg/sentry/kernel/timekeeper.go
@@ -15,6 +15,7 @@
 package kernel
 
 import (
+	"fmt"
 	"sync"
 	"time"
 
@@ -277,3 +278,28 @@ func (t *Timekeeper) GetTime(c sentrytime.ClockID) (int64, error) {
 func (t *Timekeeper) BootTime() ktime.Time {
 	return t.bootTime
 }
+
+// timekeeperClock is a ktime.Clock that reads time from a
+// kernel.Timekeeper-managed clock.
+//
+// +stateify savable
+type timekeeperClock struct {
+	tk *Timekeeper
+	c  sentrytime.ClockID
+
+	// Implements ktime.Clock.WallTimeUntil.
+	ktime.WallRateClock `state:"nosave"`
+
+	// Implements waiter.Waitable. (We have no ability to detect
+	// discontinuities from external changes to CLOCK_REALTIME).
+	ktime.NoClockEvents `state:"nosave"`
+}
+
+// Now implements ktime.Clock.Now.
+func (tc *timekeeperClock) Now() ktime.Time {
+	now, err := tc.tk.GetTime(tc.c)
+	if err != nil {
+		panic(fmt.Sprintf("timekeeperClock(ClockID=%v)).Now: %v", tc.c, err))
+	}
+	return ktime.FromNanoseconds(now)
+}