On Mon, Nov 10, 2014 at 11:21:19PM +0100, Daniel Lezcano wrote: > 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.
The ignoring it is _wrong_. Make that go away and you'll get rid of most of the STATE_START crap. The governors are the place where we combine the QoS constraints with idle predictors and pick an idle state, polling is a valid state to pick, and given QoS constraints it might be the only state to pick. > 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 ? Because the latter is actually arch specific, whereas the idle polling thing is not. You can _always_ poll idle, its generic, its valid, and its guaranteed the most responsive method. The arch drivers get to add arch specific idle states; if a x86 cpuidle driver wants to add hlt they can. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
