diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c index e592280d8acf..bba449b77641 100644 --- a/drivers/cpuidle/cpuidle-pseries.c +++ b/drivers/cpuidle/cpuidle-pseries.c @@ -346,11 +346,9 @@ static int pseries_cpuidle_driver_init(void) static void __init fixup_cede0_latency(void) { struct xcede_latency_payload *payload; - u64 min_latency_us; + u64 min_xcede_latency_us = UINT_MAX; int i; - min_latency_us = dedicated_states[1].exit_latency; // CEDE latency - if (parse_cede_parameters()) return; @@ -358,42 +356,45 @@ static void __init fixup_cede0_latency(void) nr_xcede_records); payload = &xcede_latency_parameter.payload; + + /* + * The CEDE idle state maps to CEDE(0). While the hypervisor + * does not advertise CEDE(0) exit latency values, it does + * advertise the latency values of the extended CEDE states. + * We use the lowest advertised exit latency value as a proxy + * for the exit latency of CEDE(0). + */ for (i = 0; i < nr_xcede_records; i++) { struct xcede_latency_record *record = &payload->records[i]; + u8 hint = record->hint; u64 latency_tb = be64_to_cpu(record->latency_ticks); u64 latency_us = DIV_ROUND_UP_ULL(tb_to_ns(latency_tb), NSEC_PER_USEC); - if (latency_us == 0) - pr_warn("cpuidle: xcede record %d has an unrealistic latency of 0us.\n", i); + /* + * We expect the exit latency of an extended CEDE + * state to be non-zero, it to since it takes at least + * a few nanoseconds to wakeup the idle CPU and + * dispatch the virtual processor into the Linux + * Guest. + * + * So we consider only non-zero value for performing + * the fixup of CEDE(0) latency. + */ + if (latency_us == 0) { + pr_warn("cpuidle: Skipping xcede record %d [hint=%d]. Exit latency = 0us\n", + i, hint); + continue; + } - if (latency_us < min_latency_us) - min_latency_us = latency_us; + if (latency_us < min_xcede_latency_us) + min_xcede_latency_us = latency_us; } - /* - * By default, we assume that CEDE(0) has exit latency 10us, - * since there is no way for us to query from the platform. - * - * However, if the wakeup latency of an Extended CEDE state is - * smaller than 10us, then we can be sure that CEDE(0) - * requires no more than that. - * - * Perform the fix-up. - */ - if (min_latency_us < dedicated_states[1].exit_latency) { - /* - * We set a minimum of 1us wakeup latency for cede0 to - * distinguish it from snooze - */ - u64 cede0_latency = 1; - - if (min_latency_us > cede0_latency) - cede0_latency = min_latency_us - 1; - - dedicated_states[1].exit_latency = cede0_latency; - dedicated_states[1].target_residency = 10 * (cede0_latency); + if (min_xcede_latency_us != UINT_MAX) { + dedicated_states[1].exit_latency = min_xcede_latency_us; + dedicated_states[1].target_residency = 10 * (min_xcede_latency_us); pr_info("cpuidle: Fixed up CEDE exit latency to %llu us\n", - cede0_latency); + min_xcede_latency_us); } }