Hi, 2011/8/20 Thomas Renninger <trenn@xxxxxxx>: > On Friday, August 19, 2011 05:04:04 PM tom.leiming@xxxxxxxxx wrote: >> From: Ming Lei <tom.leiming@xxxxxxxxx> >> >> This patch removes the 'cpu_id' parameter of the cpu_idle >> trace point, based on the ideas below: >> >> - the cpu_id which is passed to trace point is always the current >> cpu > Are you sure this will always be true? It is sure at least now, the only place to pass 'dev->cpu' is inside cpuidle_idle_call, but the cpuidle_device is got from __this_cpu_read(cpuidle_devices), so it should be true for such case. > >> - the current cpu info has been included into the trace result >> already >> - smp_processor_id() can't be used safely in preemptible context. > > The cpuid has been added to idle events on purpose for example to be > able to pass C-state dependencies. > 2 cores may only enter a deeper sleep state if the 2nd core enters it > as well. > There may be architectures where you could trigger a sleep state on > a foreign cpu. > > This may not be used now, but if the kernel does want to use it, you do > not want to adjust a dozen userspace apps. > > Not sure how to quickly solve the: > "smp_processor_id() can't be used safely in preemptible context." > problem, though. > A convention could be declared that if -1 is passed, it's the same cpu > entering the sleep state as the running one. This will probably > break userspace apps as well... > > Best would be to clean up x86 and let idle routines always be entered > from cpuidle subsystem which knows the cpu id already and eliminate > all idle functions in arch/x86/kernel/process.c. > > Thomas > > PS: I do not care about patch 1 and 2 as these events are ARM specific > afaik. But I vote against this one. > thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
