Changelog: v2 -> v3 * Minimal code refactoring * Rebased on v6.6-rc1 RFC v1: https://lore.kernel.org/all/20210611124154.56427-1-psampat@xxxxxxxxxxxxx/ RFC v2: https://lore.kernel.org/all/20230828061530.126588-2-aboorvad@xxxxxxxxxxxxxxxxxx/ Other related RFC: https://lore.kernel.org/all/20210430082804.38018-1-psampat@xxxxxxxxxxxxx/ Userspace selftest: https://lkml.org/lkml/2020/9/2/356 ---- A kernel module + userspace driver to estimate the wakeup latency caused by going into stop states. The motivation behind this program is to find significant deviations behind advertised latency and residency values. The patchset measures latencies for two kinds of events. IPIs and Timers As this is a software-only mechanism, there will be additional latencies of the kernel-firmware-hardware interactions. To account for that, the program also measures a baseline latency on a 100 percent loaded CPU and the latencies achieved must be in view relative to that. To achieve this, we introduce a kernel module and expose its control knobs through the debugfs interface that the selftests can engage with. The kernel module provides the following interfaces within /sys/kernel/debug/powerpc/latency_test/ for, IPI test: ipi_cpu_dest = Destination CPU for the IPI ipi_cpu_src = Origin of the IPI ipi_latency_ns = Measured latency time in ns Timeout test: timeout_cpu_src = CPU on which the timer to be queued timeout_expected_ns = Timer duration timeout_diff_ns = Difference of actual duration vs expected timer Sample output is as follows: # --IPI Latency Test--- # Baseline Avg IPI latency(ns): 2720 # Observed Avg IPI latency(ns) - State snooze: 2565 # Observed Avg IPI latency(ns) - State stop0_lite: 3856 # Observed Avg IPI latency(ns) - State stop0: 3670 # Observed Avg IPI latency(ns) - State stop1: 3872 # Observed Avg IPI latency(ns) - State stop2: 17421 # Observed Avg IPI latency(ns) - State stop4: 1003922 # Observed Avg IPI latency(ns) - State stop5: 1058870 # # --Timeout Latency Test-- # Baseline Avg timeout diff(ns): 1435 # Observed Avg timeout diff(ns) - State snooze: 1709 # Observed Avg timeout diff(ns) - State stop0_lite: 2028 # Observed Avg timeout diff(ns) - State stop0: 1954 # Observed Avg timeout diff(ns) - State stop1: 1895 # Observed Avg timeout diff(ns) - State stop2: 14556 # Observed Avg timeout diff(ns) - State stop4: 873988 # Observed Avg timeout diff(ns) - State stop5: 959137 Aboorva Devarajan (2): powerpc/cpuidle: cpuidle wakeup latency based on IPI and timer events powerpc/selftest: Add support for cpuidle latency measurement arch/powerpc/Kconfig.debug | 10 + arch/powerpc/kernel/Makefile | 1 + arch/powerpc/kernel/test_cpuidle_latency.c | 154 ++++++ tools/testing/selftests/powerpc/Makefile | 1 + .../powerpc/cpuidle_latency/.gitignore | 2 + .../powerpc/cpuidle_latency/Makefile | 6 + .../cpuidle_latency/cpuidle_latency.sh | 443 ++++++++++++++++++ .../powerpc/cpuidle_latency/settings | 1 + 8 files changed, 618 insertions(+) create mode 100644 arch/powerpc/kernel/test_cpuidle_latency.c create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/.gitignore create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/Makefile create mode 100755 tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.sh create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/settings -- 2.25.1
