On Friday, May 02, 2014 10:47:48 AM Daniel Lezcano wrote: > On 04/30/2014 01:16 AM, Rafael J. Wysocki wrote: > > On Tuesday, April 29, 2014 01:28:03 AM Rafael J. Wysocki wrote: > >> On Monday, April 28, 2014 01:14:32 PM Daniel Lezcano wrote: > >>> On 04/27/2014 02:55 PM, Rafael J. Wysocki wrote: > > [ ... ] > > > --- > > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > Subject: cpuidle / menu: Return (-1) if there are no suitable states > > > > If there is a PM QoS latency limit and all of the sufficiently shallow > > C-states are disabled, the cpuidle menu governor returns 0 which on > > some systems is CPUIDLE_DRIVER_STATE_START and shouldn't be returned > > if that C-state has been disabled. > > > > Fix the issue by modifying the menu governor to return (-1) in such > > situations. > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > --- > > drivers/cpuidle/governors/menu.c | 2 +- > > include/linux/cpuidle.h | 2 ++ > > 2 files changed, 3 insertions(+), 1 deletion(-) > > > > Index: linux-pm/drivers/cpuidle/governors/menu.c > > =================================================================== > > --- linux-pm.orig/drivers/cpuidle/governors/menu.c > > +++ linux-pm/drivers/cpuidle/governors/menu.c > > @@ -296,7 +296,7 @@ static int menu_select(struct cpuidle_dr > > data->needs_update = 0; > > } > > > > - data->last_state_idx = 0; > > + data->last_state_idx = CPUIDLE_DRIVER_STATE_START - 1; > > In case of x86, CPUIDLE_DRIVER_STATE_START will be 1, so the select > function could return 0 even this one is disabled and this is not what > you want to happen, no ?
OK, so that's a choice. We can choose to do the above or to return an error code if the 0 state is disabled too. The above is arguably simpler and matches the idea that 0 is a "fallback" state on x86. Of course, it also is confusing, because user space *can* set "disable" for the 0 state on x86, but that actually has no effect today AFAICS. I'm mostly worried about systems where CPUIDLE_DRIVER_STATE_START is 0 and where menu_select() explicitly checks "disabled" and then it returns 0 anyway if it cannot find any other suitable state. In my opinion that needs to be made consistent, but I don't care too much about which way as long as the change is not too intrusive. -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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/
