On Friday, May 02, 2014 03:19:55 PM Daniel Lezcano wrote: > On 05/02/2014 02:20 PM, Rafael J. Wysocki wrote: > > 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. > > Yes, the poll state is very rarely selected. > > Regarding the description of this patch, I think it would make sense to > move the duplicate pm qos checks to the cpuidle_idle_call function > directly and pass the latency req to the select function, so the zero > latency check could be done by the caller before entering select.
I would prefer to have them in cpuidle_select() for various reasons (one of them being to avoid the need to pass latency_req from cpuidle_idle_call() to cpuidle_select() which isn't necessary). > > 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. > > For the ARM platform, the state0 and the default idle function are the > same, so disabling this state will result in calling the same idle function. > > > 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 think we can live with this patch until we remove the > CPUIDLE_DRIVER_STATE_START macro. It was introduced to factor out a > couple of drivers and now it results in a confusing-hard-to-fix-code. OK Thanks! -- 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/
