Messages in this thread | | | Date | Mon, 10 Nov 2014 23:21:19 +0100 | From | Daniel Lezcano <> | Subject | Re: [PATCH V3 2/6] sched: idle: cpuidle: Check the latency req before idle |
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On 11/10/2014 08:48 PM, Peter Zijlstra wrote: > On Mon, Nov 10, 2014 at 06:19:02PM +0100, Daniel Lezcano wrote: >>> I really don't get why the governors should know about this though, its >>> just another state, they should iterate all states and pick the best, >>> given the power usage this state should really never be eligible unless >>> we're QoS forced or whatnot. >> >> The governors just don't use the poll state at all, except for a couple of >> cases in menu.c defined above in the previous email. What is the rational of >> adding a state in the cpuidle driver and do everything we can to avoid using >> it ? From my POV, the poll state is a special state, we should remove from >> the driver's idle states like the arch_cpu_idle() is a specific idle state >> only used in idle.c (but which may overlap with an idle state in different >> archs eg. cpu_do_idle() and the 0th idle state). > > So I disagree, I think poll-idle is an idle mode just like all the > others. It should be an available state to the governor and it should > treat it like any other.
The governors are just ignoring it, except for a small timer optimization in menu.c (and I am still not convinced it is worth to have it). I don't see the point to add a state we don't want to use.
Eg. on my server it was called 2 times over 1313856 times.
> I don't tihnk the whole ARCH_HAS_CPU_RELAX thing makes any kind of > sense, _every_ arch has some definition of it, the generic polling loop > is always a valid idle implementation. > > What we can do is always populate the idle state table with it before > calling the regular drivers.
I am not sure to understand. You want to add the poll idle loop in all the drivers ?
What about "safe_halt()" ? (arch_cpu_idle() for x86). It is also an idle state. Why not add it in the idle state table also ?
> If the arch drivers have a 'better' latency_req==0 idle routine -- note > my argument on the ppc issue, I think its wrong -- it can replace the > existing one. > > We should further remove all the special casing in the governors, its > always a valid state, but it should hardly ever be the most desirable > state. > > I think the whole arch specific idle loop is a mistake, we already have > an (arch) interface into the idle routines, we don't need yet another.
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