On Mon, 30 Apr 2018 14:42:08 +0530
Akshay Adiga <akshay.ad...@linux.vnet.ibm.com> wrote:
> Powersaving for stop0_lite and stop1_lite is observed to be quite similar
> and both states resume without state loss. Using context_switch test [1]
> we observe that stop0_lite has slightly lower latency, hence removing
> stop1_lite.
>
> [1] linux/tools/testing/selftests/powerpc/benchmarks/context_switch.c
>
> Signed-off-by: Akshay Adiga <akshay.ad...@linux.vnet.ibm.com>
I'm okay for removing stop1_lite and stop2_lite -- SMT switching
is very latency critical. If we decide to actually start saving
real power then SMT should already have been switched.
So I would put stop1_lite and stop2_lite removal in the same patch.
Then what do we have? stop0_lite, stop0, stop1 for our fast idle
states.
I would be against removing stop0 if that is our fastest way to
release SMT resources, even if there is only a small advantage. Why
not remove stop1 instead?
We also need to better evaluate stop0_lite. How much advantage does
that have over snooze?
Thanks,
Nick
> ---
> hw/slw.c | 30 ------------------------------
> 1 file changed, 30 deletions(-)
>
> diff --git a/hw/slw.c b/hw/slw.c
> index 3f9abaa..edfc783 100644
> --- a/hw/slw.c
> +++ b/hw/slw.c
> @@ -521,36 +521,6 @@ static struct cpu_idle_states power9_cpu_idle_states[] =
> {
> | OPAL_PM_PSSCR_TR(3),
> .pm_ctrl_reg_mask = OPAL_PM_PSSCR_MASK },
> {
> - .name = "stop0",
> - .latency_ns = 2000,
> - .residency_ns = 20000,
> - .flags = 0*OPAL_PM_DEC_STOP \
> - | 0*OPAL_PM_TIMEBASE_STOP \
> - | 1*OPAL_PM_LOSE_USER_CONTEXT \
> - | 0*OPAL_PM_LOSE_HYP_CONTEXT \
> - | 0*OPAL_PM_LOSE_FULL_CONTEXT \
> - | 1*OPAL_PM_STOP_INST_FAST,
> - .pm_ctrl_reg_val = OPAL_PM_PSSCR_RL(0) \
> - | OPAL_PM_PSSCR_MTL(3) \
> - | OPAL_PM_PSSCR_TR(3) \
> - | OPAL_PM_PSSCR_ESL \
> - | OPAL_PM_PSSCR_EC,
> - .pm_ctrl_reg_mask = OPAL_PM_PSSCR_MASK },
> - {
> - .name = "stop1_lite", /* Enter stop1 with no state loss */
> - .latency_ns = 4900,
> - .residency_ns = 49000,
> - .flags = 0*OPAL_PM_DEC_STOP \
> - | 0*OPAL_PM_TIMEBASE_STOP \
> - | 0*OPAL_PM_LOSE_USER_CONTEXT \
> - | 0*OPAL_PM_LOSE_HYP_CONTEXT \
> - | 0*OPAL_PM_LOSE_FULL_CONTEXT \
> - | 1*OPAL_PM_STOP_INST_FAST,
> - .pm_ctrl_reg_val = OPAL_PM_PSSCR_RL(1) \
> - | OPAL_PM_PSSCR_MTL(3) \
> - | OPAL_PM_PSSCR_TR(3),
> - .pm_ctrl_reg_mask = OPAL_PM_PSSCR_MASK },
> - {
> .name = "stop1",
> .latency_ns = 5000,
> .residency_ns = 50000,
