On Mon, Sep 04, 2017 at 01:46:45PM +0300, Alexey Budankov wrote: > > So the below completely rewrites timekeeping (and probably breaks > > world) but does away with the need to touch events that don't get > > scheduled. > > We still need and do iterate thru all events at some points e.g. on context > switches.
Why do we _need_ to? On ctx switch we should stop iteration for a PMU once we fail to schedule an event, same as for rotation. > > The basic idea is really simple, we have a single timestamp and > > depending on the state we update enabled/running. This obviously only > > requires updates when we change state and when we need up-to-date > > timestamps (read). > > I would prefer to have this rework in a FSM similar to that below, > so state transition and the corresponding tstamp, total_time_enabled > and total_time_running manipulation logic would be consolidated in > one place and adjacent lines of code. > > From the table below event->state FSM is not as simple as it may seem > on the first sight so in order to avoid regressions after rework we > better keep that in mind and explicitly implement allowed and disallowed > state transitions. Maybe if we introduce something like CONFIG_PERF_DEBUG, but I fear that for normal operation that's all fairly horrible overhead. > A I O E X D U > > A Te+,Tr+ Te+,Tr+ Te+,Tr+ Te+,Tr+ Te+,Tr+ Te+,Tr+ --- > ts ts ts ts ts ts > > I Te+,ts Te+,ts Te+,ts Te+,ts Te+,ts Te+,ts --- > > O Te=0,Tr=0, Te=0,Tr=0, Te=0,Tr=0 Te=0,Tr=0 Te=0,Tr=0 Te=0,Tr=0 --- > ts ts ts ts ts ts > > E Te=0,Tr=0, Te=0,Tr=0, Te=0,Tr=0 Te=0,Tr=0 Te=0,Tr=0 Te=0,Tr=0 --- > ts ts ts ts ts ts > > X --- --- --- --- --- --- --- > > D --- --- --- --- --- --- --- > > U --- Te=0,Tr=0 Te=0,Tr=0 --- --- --- --- > ts ts > > LEGEND: > > U - allocation, A - ACTIVE, I - INACTIVE, O - OFF, > E - ERROR, X - EXIT, D - DEAD, Not sure we care about the different <0 values, they're all effectively OFF.
