| Date | Thu, 30 Apr 2015 21:17:51 +0100 | From | Dietmar Eggemann <> | Subject | Re: [RFCv3 PATCH 37/48] sched: Determine the current sched_group idle-state |
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On 30/04/15 06:12, pang.xunlei@zte.com.cn wrote: > linux-kernel-owner@vger.kernel.org wrote 2015-02-05 AM 02:31:14: > >> Morten Rasmussen <morten.rasmussen@arm.com> >> >> [RFCv3 PATCH 37/48] sched: Determine the current sched_group idle-state >> >> To estimate the energy consumption of a sched_group in >> sched_group_energy() it is necessary to know which idle-state the group >> is in when it is idle. For now, it is assumed that this is the current >> idle-state (though it might be wrong). Based on the individual cpu >> idle-states group_idle_state() finds the group idle-state.
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>> +static int group_idle_state(struct sched_group *sg) >> +{ >> + struct sched_group_energy *sge = sg->sge; >> + int shallowest_state = sge->idle_states_below + sge->nr_idle_states; >> + int i; >> + >> + for_each_cpu(i, sched_group_cpus(sg)) { >> + int cpuidle_idx = idle_get_state_idx(cpu_rq(i)); >> + int group_idx = cpuidle_idx - sge->idle_states_below + 1; > > So cpuidle_idx==0 for core-level(2 C-States for example) groups, it > returns 1?
Yes.
> > What does this mean?
So for ARM TC2 and CPU0 (Cortex A15, big) for example:
# cat /sys/devices/system/cpu/cpu0/cpuidle/state*/name WFI [cpuidle_idx=0] cluster-sleep-b [cpuidle_idx=1]
group_idx is the system C state re-indexed to the sd (e.g.on MC level WFI is group idx 1 and on DIE level it's group idx 0).
For MC (or core-) level groups:
cpu=0 sg_mask=0x1 group_idx=1 cpuidle_idx=0 sge->idle_states_below=0 shallowest_state=1 sge->nr_idle_states=1
group_idle_state() returns 0 in this case because of (shallowest_state=1 >= sge->nr_idle_states=1).
This value is then used to index into the sg->sge->idle_states[] to get the idle power value for the topology bit represented by sg (i.e. for CPU0). The idle power value for CPU0 is originally specified in the energy model:
static struct idle_state idle_states_core_a15[] = { .power = 0 }, }; [arch/arm/kernel/topology.c]
Another example would be to find the idle power value for the LITTLE cluster if it is in 'cluster-sleep-l' [cpuidle_idx=1]:
cpu=2 sg_mask=0x1c group_idx=1 cpuidle_idx=1 sge->idle_states_below=1 shallowest_state=3 sge->nr_idle_states=2 cpu=3 sg_mask=0x1c group_idx=1 cpuidle_idx=1 sge->idle_states_below=1 shallowest_state=1 sge->nr_idle_states=2 cpu=3 sg_mask=0x1c group_idx=1 cpuidle_idx=1 sge->idle_states_below=1 shallowest_state=1 sge->nr_idle_states=2
group_idle_state() returns 1 (shallowest_state=1) and the idle power value is 10.
static struct idle_state idle_states_cluster_a7[] = { ..., { .power = 10 }};
To sum it up, group_idle_state() is necessary to transform the C state values (-1, 0, 1) into sg->sge->idle_states[] indexes for the different sg's (MC, DIE).
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