On Tue, 2015-03-17 at 21:19 +0530, Shreyas B Prabhu wrote: > > On Tuesday 17 March 2015 03:09 PM, Benjamin Herrenschmidt wrote: > > On Tue, 2015-03-17 at 19:57 +1100, Michael Ellerman wrote: > >> > >> >From what I can see below, the decision as to whether you apply the > >> >workaround > >> or not doesn't affect the list of idle states. So this could just as well > >> be a > >> runtime parameter, ie. a sysfs file, which can then be set by the user > >> whenever > >> they like? They might do it in a boot script, but that's up to them. > > > > Right, that would work too. > > Okay. I'll send a patch with this design.
Thanks. > >> For simplicity I think it would also be fine to make it a write-once > >> parameter, > >> ie. you don't need to handle undoing it. > > > > It would be easy enough to make it rw using stop machine I think... > > > >> I think the only complication that would add is that you'd need to be a > >> little > >> careful about the order in which you nop out the calls vs applying the > >> workaround, in case some threads are idle when you're called. > > Right, we should be safe with this sequence- > - NOP call to undo workaround > - Apply workaround on all cores. > - NOP call to apply workaround Yeah that sounds right. > > I wouldn't bother with NOP'ing in that case, a runtime test will probably > > be noise > > in the measurement. > > Didn't get your point here. Do you mean, ignore the request if some > cores are in sleep or deeper state? I *think* what he means is we probably don't actually need to patch a nop in/out. Instead we could just test a flag, because the cost of testing a flag is miniscule compared to the rest of the logic. cheers -- 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/
