30/06/2017 10:52, Van Haaren, Harry: > From: Thomas Monjalon [mailto:tho...@monjalon.net] > > 29/06/2017 18:35, Van Haaren, Harry: > > > 3) The problem; > > > If a service core runs the SW PMD schedule() function (option 2) *AND* > > > the application lcore runs schedule() func (option 1), the result is > > > that > > > two threads are concurrently running a multi-thread unsafe function. > > > > Which function is multi-thread unsafe? > > With the current design, the service-callback does not have to be > multi-thread safe. > For example, the eventdev SW PMD is not multi-thread safe. > > The service library handles serializing access to the service-callback if > multiple cores > are mapped to that service. This keeps the atomic complexity in one place, > and keeps > services as light-weight to implement as possible. > > (We could consider forcing all service-callbacks to be multi-thread safe by > using atomics, > but we would not be able to optimize away the atomic cmpset if it is not > required. This > feels heavy handed, and would cause useless atomic ops to execute.)
OK thank you for the detailed explanation. > > Why the same function would be run by the service and by the scheduler? > > The same function can be run concurrently by the application, and a service > core. > The root cause that this could happen is that an application can *think* it > is the > only one running threads, but in reality one or more service-cores may be > running > in the background. > > The service lcores and application lcores existence without knowledge of the > others > behavior is the cause of concurrent running of the multi-thread unsafe > service function. That's the part I still don't understand. Why an application would run a function on its own core if it is already run as a service? Can we just have a check that the service API exists and that the service is running?
