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.