Re: [Skiboot] [PATCH 1/2] SLW: Remove stop1_lite and stop0 stop states
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2018-05-01 03:47:23
On Mon, 30 Apr 2018 14:42:08 +0530 Akshay Adiga [off-list ref] 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 <redacted>
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
quoted hunk
--- 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,