On Sat, 2008-02-02 at 02:39 -0500, Len Brown wrote: > On Monday 28 January 2008 00:55, Zhao Yakui wrote: > > Subject: ACPI : Update the t-state for every affected cpu when t-state is > > changed > > >From : Zhao Yakui <[EMAIL PROTECTED]> > > > > According to ACPI spec, the _TSD object provides T-state control cross > > logical processor dependency information to OSPM. So the t-state > > coordination should be considered when T-state for one cpu is changed. > > > > According to ACPI spec, three types of coordination are defined. > > SW_ALL, SW_ANY and HW_ALL. > > > SW_ALL: it means that OSPM needs to initiate T-state transition on > > all processors in the domain. It is necessary to call throttling set > > function > > for all affected cpus. > > > SW_ANY: it means that OSPM may initiate T-state transition on any processor > > in > > the domain. > > > HW_ALL: Apec only says that hardware will perform the coordination and > > doesn't > > recommend how OSPM coordinate T-state among the affected cpus. So it is > > treated > > as the type of SW_ALL. It means that OSPM needs to initiate t-state > > transition > > on all the processors in the domain. > > Not really. HW_ALL means that the OS can assume that the CPUs are independent, > and hardware will take care of any coordination needed. Hardware will be responsible for coordinating the state transition between multiple processors. But hardware should provide OSPM with a means to determine the actual state residency so that the correct state is entered. > > ie. the OS should implement throttling changes on each CPU depending > only on that CPU's needs and not need to consider any effects on other CPUs. > > This is not the same as SW_ALL, which tells us that all the CPUS in a domain > are _dependent_, and the OS must enforce that by writing the _same_ value > to each CPU. > > say you have a domain with 2 CPUS. > If it is HW_ALL and you throttle one cpu, then you are done. In this case , how to update the state of another cpu? Can it be treated as SW_ANY? > if it is SW_ALL then if you want to throttle one cpu, then you must > also throttle the other. I agree. It is necessary to initiate the state transition for every affected cpu. > > -Len
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