v2: https://lkml.org/lkml/2020/7/17/369 Changelog v2-->v3 Based on comments from Gautham R. Shenoy adding the following in the selftest, 1. Grepping modules to determine if already loaded 2. Wrapper to enable/disable states 3. Preventing any operation/test on offlined CPUs --- The patch series introduces a mechanism to measure wakeup latency for IPI and timer based interrupts The motivation behind this series is to find significant deviations behind advertised latency and resisdency values 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/latency_test/ for, 1. 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 2. 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 To include the module, check option and include as module kernel hacking -> Cpuidle latency selftests The selftest inserts the module, disables all the idle states and enables them one by one testing the following: 1. Keeping source CPU constant, iterates through all the CPUS measuring IPI latency for baseline (CPU is busy with "cat /dev/random > /dev/null" workload) and the when the CPU is allowed to be at rest 2. Iterating through all the CPUs, sending expected timer durations to be equivalent to the residency of the the deepest idle state enabled and extracting the difference in time between the time of wakeup and the expected timer duration Usage ----- Can be used in conjuction to the rest of the selftests. Default Output location in: tools/testing/cpuidle/cpuidle.log To run this test specifically: $ make -C tools/testing/selftests TARGETS="cpuidle" run_tests There are a few optinal arguments too that the script can take [-h <help>] [-m <location of the module>] [-o <location of the output>] Sample output snippet --------------------- --IPI Latency Test--- --Baseline IPI Latency measurement: CPU Busy-- SRC_CPU DEST_CPU IPI_Latency(ns) ... 0 8 1996 0 9 2125 0 10 1264 0 11 1788 0 12 2045 Baseline Average IPI latency(ns): 1843 ---Enabling state: 5--- SRC_CPU DEST_CPU IPI_Latency(ns) 0 8 621719 0 9 624752 0 10 622218 0 11 623968 0 12 621303 Expected IPI latency(ns): 100000 Observed Average IPI latency(ns): 622792 --Timeout Latency Test-- --Baseline Timeout Latency measurement: CPU Busy-- Wakeup_src Baseline_delay(ns) ... 8 2249 9 2226 10 2211 11 2183 12 2263 Baseline Average timeout diff(ns): 2226 ---Enabling state: 5--- 8 10749 9 10911 10 10912 11 12100 12 73276 Expected timeout(ns): 10000200 Observed Average timeout diff(ns): 23589 Pratik Rajesh Sampat (2): cpuidle: Trace IPI based and timer based wakeup latency from idle states selftest/cpuidle: Add support for cpuidle latency measurement drivers/cpuidle/Makefile | 1 + drivers/cpuidle/test-cpuidle_latency.c | 150 ++++++++++ lib/Kconfig.debug | 10 + tools/testing/selftests/Makefile | 1 + tools/testing/selftests/cpuidle/Makefile | 6 + tools/testing/selftests/cpuidle/cpuidle.sh | 310 +++++++++++++++++++++ tools/testing/selftests/cpuidle/settings | 1 + 7 files changed, 479 insertions(+) create mode 100644 drivers/cpuidle/test-cpuidle_latency.c create mode 100644 tools/testing/selftests/cpuidle/Makefile create mode 100755 tools/testing/selftests/cpuidle/cpuidle.sh create mode 100644 tools/testing/selftests/cpuidle/settings -- 2.25.4
