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Skip itimer "fairness" tests on ptrace.

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With additional logging, the issue described by the new comment looks like:

D0518 21:28:08.416810    6777 task_signals.go:459] [   8] Notified of signal 27
D0518 21:28:08.416852    6777 task_block.go:223] [   8] Interrupt queued
D0518 21:28:08.417013    6777 task_run.go:250] [   8] Switching to sentry
D0518 21:28:08.417033    6777 task_signals.go:220] [   8] Signal 27: delivering to handler
D0518 21:28:08.417127    6777 task_run.go:248] [   8] Switching to app
D0518 21:28:08.443765    6777 task_signals.go:519] [   8] Refusing masked signal 27 // ED: note the ~26ms elapsed since TID 8 "switched to app"
D0518 21:28:08.443814    6777 task_signals.go:465] [   6] Notified of group signal 27
D0518 21:28:08.443832    6777 task_block.go:223] [   6] Interrupt queued
D0518 21:28:08.443914    6777 task_block.go:223] [   6] Interrupt queued
D0518 21:28:08.443859    6777 task_run.go:250] [   8] Switching to sentry
I0518 21:28:08.443936    6777 strace.go:576] [   8] exe E rt_sigreturn()

Slow context switches on ptrace are probably due to kernel scheduling delays.
Slow context switches on KVM are less clear, so leave that bug and TODO open.

PiperOrigin-RevId: 312322782
This commit is contained in:
Jamie Liu
2020-05-19 11:53:03 -07:00
committed by gVisor bot
parent d06de1bede
commit 064347afdf
1 changed files with 17 additions and 4 deletions
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test/syscalls/linux/itimer.cc
+17 -4
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@@ -267,8 +267,19 @@ int TestSIGPROFFairness(absl::Duration sleep) {
// Random save/restore is disabled as it introduces additional latency and
// unpredictable distribution patterns.
TEST(ItimerTest, DeliversSIGPROFToThreadsRoughlyFairlyActive_NoRandomSave) {
// TODO(b/143247272): CPU time accounting is inaccurate for the KVM platform.
SKIP_IF(GvisorPlatform() == Platform::kKVM);
// On the KVM and ptrace platforms, switches between sentry and application
// context are sometimes extremely slow, causing the itimer to send SIGPROF to
// a thread that either already has one pending or has had SIGPROF delivered,
// but hasn't handled it yet (and thus therefore still has SIGPROF masked). In
// either case, since itimer signals are group-directed, signal sending falls
// back to notifying the thread group leader. ItimerSignalTest() fails if "too
// many" signals are delivered to the thread group leader, so these tests are
// flaky on these platforms.
//
// TODO(b/143247272): Clarify why context switches are so slow on KVM.
const auto gvisor_platform = GvisorPlatform();
SKIP_IF(gvisor_platform == Platform::kKVM ||
gvisor_platform == Platform::kPtrace);
pid_t child;
int execve_errno;
@@ -291,8 +302,10 @@ TEST(ItimerTest, DeliversSIGPROFToThreadsRoughlyFairlyActive_NoRandomSave) {
// Random save/restore is disabled as it introduces additional latency and
// unpredictable distribution patterns.
TEST(ItimerTest, DeliversSIGPROFToThreadsRoughlyFairlyIdle_NoRandomSave) {
// TODO(b/143247272): CPU time accounting is inaccurate for the KVM platform.
SKIP_IF(GvisorPlatform() == Platform::kKVM);
// See comment in DeliversSIGPROFToThreadsRoughlyFairlyActive.
const auto gvisor_platform = GvisorPlatform();
SKIP_IF(gvisor_platform == Platform::kKVM ||
gvisor_platform == Platform::kPtrace);
pid_t child;
int execve_errno;