On Mon, 2023-09-25 at 10:36 +0530, Aboorva Devarajan wrote: Gentle ping to check if there are any feedback or comments on this patch-set. Thanks Aboorva > On Mon, 2023-09-11 at 11:06 +0530, Aboorva Devarajan wrote: > > CC'ing CPUidle lists and maintainers, > > Patch Summary: > > The patchset introduces a kernel module and userspace driver designed > for estimating the wakeup latency experienced when waking up from > various CPU idle states. It primarily measures latencies related to > two > types of events: Inter-Processor Interrupts (IPIs) and Timers. > > Background: > > Initially, these patches were introduced as a generic self-test. > However, it was later discovered that Intel platforms incorporate > timer-based wakeup optimizations. These optimizations allow CPUs to > perform a pre-wakeup, which limits the effectiveness of latency > observation in certain scenarios because it only measures the > optimized > wakeup latency [1]. > > Therefore, in this RFC, the self-test is specifically integrated into > PowerPC, as it has been tested and used in PowerPC so far. > > Another proposal is to introduce these patches as a generic cpuilde > IPI > and timer wake-up test. While this method may not give us an exact > measurement of latency variations at the hardware level, it can still > help us assess this metric from a software observability standpoint. > > Looking forward to hearing what you think and any suggestions you may > have regarding this. Thanks. > > [1] > https://lore.kernel.org/linux-pm/20200914174625.GB25628@xxxxxxxxxx/T/#m5c004b9b1a918f669e91b3d0f33e2e3500923234 > > > 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 > >
