Messages in this thread | | | Date | Fri, 31 Jan 2014 17:35:45 +0100 | From | Daniel Lezcano <> | Subject | Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq |
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On 01/31/2014 04:50 PM, Arjan van de Ven wrote: > On 1/31/2014 7:37 AM, Daniel Lezcano wrote: >> On 01/31/2014 04:07 PM, Arjan van de Ven wrote: >>>>>> >>>>>> Hence I think this patch would make sense only with additional >>>>>> information >>>>>> like exit_latency or target_residency is present for the scheduler. >>>>>> The idle >>>>>> state index alone will not be sufficient. >>>>> >>>>> Alternatively, can we enforce sanity on the cpuidle infrastructure to >>>>> make the index naturally ordered? If not, please explain why :-) >>>> >>>> The commit id 71abbbf856a0e70 says that there are SOCs which could have >>>> their target_residency and exit_latency values change at runtime. This >>>> commit thus removed the ordering of the idle states according to their >>>> target_residency/exit_latency. Adding Len and Arjan to the CC. >>> >>> the ARM folks wanted a dynamic exit latency, so.... it makes much more >>> sense >>> to me to store the thing you want to use (exit latency) than the number >>> of the state. >>> >>> more than that, you can order either by target residency OR by exit >>> latency, >>> if you sort by one, there is no guarantee that you're also sorted by the >>> other >> >> IMO, it would be preferable to store the index for the moment as we >> are integrating cpuidle with the scheduler. The index allows to access >> more informations. Then when >> everything is fully integrated we can improve the result, no ? > > more information, yes. but if the information isn't actually accurate > (because it keeps changing > in the datastructure away from what it was for the cpu)... are you > really achieving what you want? > > on x86 I don't care; we don't actually change these dynamically much[1]. > But if you have 1 or 2 things in mind to use, > I would suggest copying those 2 integers instead as we go, rather than > the index. > Saves refcounting/locking etc etc nightmare as well on the other > subsystems' datastructures.. > ... which you likely need to do to actually follow that index.
Hmm, yeah. That's a fair argument. That is true, the races and locks/refcnt are something we have to worried about. But also we may want to prevent duplicating the data across the subsystems.
> [1] Although in an ACPI world, the total number of C states can vary, > for example it used to be quite common > that you got an extra C state on battery versus on wall power. This sort > of dynamic thing requires refcounting > if more than the local cpuidle uses the data structures. >
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