On 2024/9/26 7:24, Ankur Arora wrote: > This patchset enables the cpuidle-haltpoll driver and its namesake > governor on arm64. This is specifically interesting for KVM guests by > reducing IPC latencies. > > Comparing idle switching latencies on an arm64 KVM guest with > perf bench sched pipe: > > usecs/op %stdev > > no haltpoll (baseline) 13.48 +- 5.19% > with haltpoll 6.84 +- 22.07% > > > No change in performance for a similar test on x86: > > usecs/op %stdev > > haltpoll w/ cpu_relax() (baseline) 4.75 +- 1.76% > haltpoll w/ smp_cond_load_relaxed() 4.78 +- 2.31% > > Both sets of tests were on otherwise idle systems with guest VCPUs > pinned to specific PCPUs. One reason for the higher stdev on arm64 > is that trapping of the WFE instruction by the host KVM is contingent > on the number of tasks on the runqueue. > > Tomohiro Misono and Haris Okanovic also report similar latency > improvements on Grace and Graviton systems (for v7) [1] [2]. > > The patch series is organized in three parts: > > - patch 1, reorganizes the poll_idle() loop, switching to > smp_cond_load_relaxed() in the polling loop. > Relatedly patches 2, 3 mangle the config option ARCH_HAS_CPU_RELAX, > renaming it to ARCH_HAS_OPTIMIZED_POLL. > > - patches 4-6 reorganize the haltpoll selection and init logic > to allow architecture code to select it. > > - and finally, patches 7-11 add the bits for arm64 support. > > What is still missing: this series largely completes the haltpoll side > of functionality for arm64. There are, however, a few related areas > that still need to be threshed out: > > - WFET support: WFE on arm64 does not guarantee that poll_idle() > would terminate in halt_poll_ns. Using WFET would address this. > - KVM_NO_POLL support on arm64 > - KVM TWED support on arm64: allow the host to limit time spent in > WFE. > > > Changelog: > > v8: No logic changes. Largely respin of v7, with changes > noted below: > > - move selection of ARCH_HAS_OPTIMIZED_POLL on arm64 to its > own patch. > (patch-9 "arm64: select ARCH_HAS_OPTIMIZED_POLL") > > - address comments simplifying arm64 support (Will Deacon) > (patch-11 "arm64: support cpuidle-haltpoll") > > v7: No significant logic changes. Mostly a respin of v6. > > - minor cleanup in poll_idle() (Christoph Lameter) > - fixes conflicts due to code movement in arch/arm64/kernel/cpuidle.c > (Tomohiro Misono) > > v6: > > - reordered the patches to keep poll_idle() and ARCH_HAS_OPTIMIZED_POLL > changes together (comment from Christoph Lameter) > - threshes out the commit messages a bit more (comments from Christoph > Lameter, Sudeep Holla) > - also rework selection of cpuidle-haltpoll. Now selected based > on the architectural selection of ARCH_CPUIDLE_HALTPOLL. > - moved back to arch_haltpoll_want() (comment from Joao Martins) > Also, arch_haltpoll_want() now takes the force parameter and is > now responsible for the complete selection (or not) of haltpoll. > - fixes the build breakage on i386 > - fixes the cpuidle-haltpoll module breakage on arm64 (comment from > Tomohiro Misono, Haris Okanovic) > > > v5: > - rework the poll_idle() loop around smp_cond_load_relaxed() (review > comment from Tomohiro Misono.) > - also rework selection of cpuidle-haltpoll. Now selected based > on the architectural selection of ARCH_CPUIDLE_HALTPOLL. > - arch_haltpoll_supported() (renamed from arch_haltpoll_want()) on > arm64 now depends on the event-stream being enabled. > - limit POLL_IDLE_RELAX_COUNT on arm64 (review comment from Haris Okanovic) > - ARCH_HAS_CPU_RELAX is now renamed to ARCH_HAS_OPTIMIZED_POLL. > > v4 changes from v3: > - change 7/8 per Rafael input: drop the parens and use ret for the final check > - add 8/8 which renames the guard for building poll_state > > v3 changes from v2: > - fix 1/7 per Petr Mladek - remove ARCH_HAS_CPU_RELAX from arch/x86/Kconfig > - add Ack-by from Rafael Wysocki on 2/7 > > v2 changes from v1: > - added patch 7 where we change cpu_relax with smp_cond_load_relaxed per PeterZ > (this improves by 50% at least the CPU cycles consumed in the tests above: > 10,716,881,137 now vs 14,503,014,257 before) > - removed the ifdef from patch 1 per RafaelW > > Please review. > > [1] https://lore.kernel.org/lkml/TY3PR01MB111481E9B0AF263ACC8EA5D4AE5BA2@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > [2] https://lore.kernel.org/lkml/104d0ec31cb45477e27273e089402d4205ee4042.camel@xxxxxxxxxx/ > > Ankur Arora (6): > cpuidle: rename ARCH_HAS_CPU_RELAX to ARCH_HAS_OPTIMIZED_POLL > cpuidle-haltpoll: condition on ARCH_CPUIDLE_HALTPOLL > arm64: idle: export arch_cpu_idle > arm64: select ARCH_HAS_OPTIMIZED_POLL > cpuidle/poll_state: limit POLL_IDLE_RELAX_COUNT on arm64 > arm64: support cpuidle-haltpoll > > Joao Martins (4): > Kconfig: move ARCH_HAS_OPTIMIZED_POLL to arch/Kconfig > cpuidle-haltpoll: define arch_haltpoll_want() > governors/haltpoll: drop kvm_para_available() check > arm64: define TIF_POLLING_NRFLAG > > Mihai Carabas (1): > cpuidle/poll_state: poll via smp_cond_load_relaxed() > > arch/Kconfig | 3 +++ > arch/arm64/Kconfig | 7 +++++++ > arch/arm64/include/asm/cpuidle_haltpoll.h | 24 +++++++++++++++++++++++ > arch/arm64/include/asm/thread_info.h | 2 ++ > arch/arm64/kernel/idle.c | 1 + > arch/x86/Kconfig | 5 ++--- > arch/x86/include/asm/cpuidle_haltpoll.h | 1 + > arch/x86/kernel/kvm.c | 13 ++++++++++++ > drivers/acpi/processor_idle.c | 4 ++-- > drivers/cpuidle/Kconfig | 5 ++--- > drivers/cpuidle/Makefile | 2 +- > drivers/cpuidle/cpuidle-haltpoll.c | 12 +----------- > drivers/cpuidle/governors/haltpoll.c | 6 +----- > drivers/cpuidle/poll_state.c | 22 +++++++++++++++------ > drivers/idle/Kconfig | 1 + > include/linux/cpuidle.h | 2 +- > include/linux/cpuidle_haltpoll.h | 5 +++++ > 17 files changed, 83 insertions(+), 32 deletions(-) > create mode 100644 arch/arm64/include/asm/cpuidle_haltpoll.h > Hi Ankur, Thanks for the patches! We have tested these patches on our machine, with an adaptation of ACPI LPI states rather than c-states. Include polling state, there would be three states to get in. Comparing idle switching latencies of different state with perf bench sched pipe: usecs/op %stdev state0(polling state) 7.36 +- 0.35% state1 8.78 +- 0.46% state2 77.32 +- 5.50% It turns out that it works on our machine. Tested-by: Lifeng Zheng <zhenglifeng1@xxxxxxxxxx> The adaptation of ACPI LPI states is shown below as a patch. Feel free to include this patch as part of your series, or I can also send it out after your series being merged. From: Lifeng Zheng <zhenglifeng1@xxxxxxxxxx> ACPI: processor_idle: Support polling state for LPI Initialize an optional polling state besides LPI states. Wrap up a new enter method to correctly reflect the actual entered state when the polling state is enabled. Signed-off-by: Lifeng Zheng <zhenglifeng1@xxxxxxxxxx> Reviewed-by: Jie Zhan <zhanjie9@xxxxxxxxxxxxx> --- drivers/acpi/processor_idle.c | 39 ++++++++++++++++++++++++++++++----- 1 file changed, 34 insertions(+), 5 deletions(-) diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index 44096406d65d..d154b5d77328 100644 --- a/drivers/acpi/processor_idle.c +++ b/drivers/acpi/processor_idle.c @@ -1194,20 +1194,46 @@ static int acpi_idle_lpi_enter(struct cpuidle_device *dev, return -EINVAL; } +/* To correctly reflect the entered state if the poll state is enabled. */ +static int acpi_idle_lpi_enter_with_poll_state(struct cpuidle_device *dev, + struct cpuidle_driver *drv, int index) +{ + int entered_state; + + if (unlikely(index < 1)) + return -EINVAL; + + entered_state = acpi_idle_lpi_enter(dev, drv, index - 1); + if (entered_state < 0) + return entered_state; + + return entered_state + 1; +} + static int acpi_processor_setup_lpi_states(struct acpi_processor *pr) { - int i; + int i, count; struct acpi_lpi_state *lpi; struct cpuidle_state *state; struct cpuidle_driver *drv = &acpi_idle_driver; + typeof(state->enter) enter_method; if (!pr->flags.has_lpi) return -EOPNOTSUPP; + if (IS_ENABLED(CONFIG_ARCH_HAS_OPTIMIZED_POLL)) { + cpuidle_poll_state_init(drv); + count = 1; + enter_method = acpi_idle_lpi_enter_with_poll_state; + } else { + count = 0; + enter_method = acpi_idle_lpi_enter; + } + for (i = 0; i < pr->power.count && i < CPUIDLE_STATE_MAX; i++) { lpi = &pr->power.lpi_states[i]; - state = &drv->states[i]; + state = &drv->states[count]; snprintf(state->name, CPUIDLE_NAME_LEN, "LPI-%d", i); strscpy(state->desc, lpi->desc, CPUIDLE_DESC_LEN); state->exit_latency = lpi->wake_latency; @@ -1215,11 +1241,14 @@ static int acpi_processor_setup_lpi_states(struct acpi_processor *pr) state->flags |= arch_get_idle_state_flags(lpi->arch_flags); if (i != 0 && lpi->entry_method == ACPI_CSTATE_FFH) state->flags |= CPUIDLE_FLAG_RCU_IDLE; - state->enter = acpi_idle_lpi_enter; - drv->safe_state_index = i; + state->enter = enter_method; + drv->safe_state_index = count; + count++; + if (count == CPUIDLE_STATE_MAX) + break; } - drv->state_count = i; + drv->state_count = count; return 0; } -- 2.33.0
