On Wed, 18 Jun 2014, Santosh Shilimkar wrote: > On Wednesday 18 June 2014 04:51 PM, Nicolas Pitre wrote: > > On Wed, 18 Jun 2014, Santosh Shilimkar wrote: > > > >> On Wednesday 18 June 2014 01:36 PM, Lorenzo Pieralisi wrote: > >> [..] > >>> + To correctly specify idle states timing and energy related properties, > >>> + the following definitions identify the different execution phases > >>> + a CPU goes through to enter and exit idle states and the implied > >>> + energy metrics: > >>> + > >>> + ..__[EXEC]__|__[PREP]__|__[ENTRY]__|__[IDLE]__|__[EXIT]__|__[EXEC]__.. > >>> + | | | | | > >>> + > >>> + |<------ entry ------->| > >>> + | latency | > >>> + |<- exit ->| > >>> + | latency | > >>> + |<-------- min-residency -------->| > >>> + |<------- wakeup-latency ------->| > >>> + > >> I don't know the wakeup latency makes much sense and also correct. > >> Hardware wakeup latency is actually exit latency. Is it for failed > >> or abort-able ilde case ? We are adding this as a new parameter > >> at least from idle states perspective. I think we should just > >> avoid it. > > > > I explained the rationale for this parameter in a previous email but > > Lorenzo didn't carry it over. To be clearer, this should be "worst case > > wake-up latency". It is of interest for PMQOS. This is the maximum > > delay that can be expected from the moment a wake-up event is signaled > > and the moment the CPU is back operational. This is more than just exit > > latency. By default this is entry_latency + exit_latency but when there > > is an abortable PREP phase then it may be shorter than that. > > > PMQOS angle is right. It is just that the idle code is not > going to do anything with this value. But I see a value adding it > instead of some one doing calculation. The idle code should take it into account when a PMQOS restriction is in effect i.e. avoid using those modes whose worst case wake-up latency is too large. And cpuidle is being migrated into the scheduler as we speak. So some of the values there, namely entry_latency and exit_latency (taken separately for timing purposes) will be directly used by the scheduler to decide which CPU to wake up for example. So there is fundamentally 4 parameters if we want to comprehensively support all pertinent use cases. Nicolas -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
