* Gautham R Shenoy <[email protected]> [2020-07-07 16:41:39]: > From: "Gautham R. Shenoy" <[email protected]> > > The Extended CEDE state with latency-hint = 1 is only different from > normal CEDE (with latency-hint = 0) in that a CPU in Extended CEDE(1) > does not wakeup on timer events. Both CEDE and Extended CEDE(1) map to > the same hardware idle state. Since we already get SMT folding from > the normal CEDE, the Extended CEDE(1) doesn't provide any additional > value. This patch blocks Extended CEDE(1). > > Signed-off-by: Gautham R. Shenoy <[email protected]>
Reviewed-by: Vaidyanathan Srinivasan <[email protected]> > --- > drivers/cpuidle/cpuidle-pseries.c | 57 > ++++++++++++++++++++++++++++++++++++--- > 1 file changed, 54 insertions(+), 3 deletions(-) > > diff --git a/drivers/cpuidle/cpuidle-pseries.c > b/drivers/cpuidle/cpuidle-pseries.c > index 6f893cd..be0b8b2 100644 > --- a/drivers/cpuidle/cpuidle-pseries.c > +++ b/drivers/cpuidle/cpuidle-pseries.c > @@ -350,6 +350,43 @@ static int pseries_cpuidle_driver_init(void) > return 0; > } > > +#define XCEDE1_HINT 1 > +#define ERR_NO_VALUE_ADD (-1) > +#define ERR_NO_EE_WAKEUP (-2) > + > +/* > + * Returns 0 if the Extende CEDE state with @hint is not blocked in > + * cpuidle framework. > + * > + * Returns ERR_NO_EE_WAKEUP if the Extended CEDE state is blocked due > + * to not being responsive to external interrupts. > + * > + * Returns ERR_NO_VALUE_ADD if the Extended CEDE state does not provide > + * added value addition over the normal CEDE. > + */ > +static int cpuidle_xcede_blocked(u8 hint, u64 latency_us, u8 > responsive_to_irqs) > +{ > + > + /* > + * We will only allow extended CEDE states that are responsive > + * to irqs do not require an H_PROD to be woken up. > + */ > + if (!responsive_to_irqs) > + return ERR_NO_EE_WAKEUP; > + > + /* > + * We already obtain SMT folding benefits from CEDE (which is > + * CEDE with hint 0). Furthermore, CEDE is also responsive to > + * timer-events, while XCEDE1 requires an external > + * interrupt/H_PROD to be woken up. Hence, block XCEDE1 since > + * it adds no further value. > + */ > + if (hint == XCEDE1_HINT) > + return ERR_NO_VALUE_ADD; > + > + return 0; > +} > + > static int add_pseries_idle_states(void) > { > int nr_states = 2; /* By default we have snooze, CEDE */ > @@ -365,15 +402,29 @@ static int add_pseries_idle_states(void) > char name[CPUIDLE_NAME_LEN]; > unsigned int latency_hint = xcede_records[i].latency_hint; > u64 residency_us; > + int rc; > + > + if (latency_us < min_latency_us) > + min_latency_us = latency_us; > + > + rc = cpuidle_xcede_blocked(latency_hint, latency_us, > + xcede_records[i].responsive_to_irqs); > > - if (!xcede_records[i].responsive_to_irqs) { > + if (rc) { > + switch (rc) { > + case ERR_NO_VALUE_ADD: > + pr_info("cpuidle : Skipping XCEDE%d. No > additional value-add\n", > + latency_hint); > + break; > + case ERR_NO_EE_WAKEUP: > pr_info("cpuidle : Skipping XCEDE%d. Not responsive to > IRQs\n", > latency_hint); > + break; > + } > + > continue; > } > > - if (latency_us < min_latency_us) > - min_latency_us = latency_us; > snprintf(name, CPUIDLE_NAME_LEN, "XCEDE%d", latency_hint); > > /* We need these heuristics to select/reject idle states exposed by platform firmware to Linux primarily because not all states are really useful to Linux on a given setup. --Vaidy
