26/02/2021 00:33, Honnappa Nagarahalli: > +Thomas, David, Konstantin for input > > <snip> > > > > Subject: [RFC 3/5] eal: lcore state FINISHED is not required > > > > > > FINISHED state seems to be used to indicate that the worker's update > > > of the 'state' is not visible to other threads. There seems to be no > > > requirement to have such a state. > > > > I am not sure "FINISHED" is necessary to be removed, and I propose some of > > my > > profiles for discussion. > > There are three states for lcore now: > > "WAIT": indicate lcore can start working > > "RUNNING": indicate lcore is working > > "FINISHED": indicate lcore has finished its working and wait to be reset > If you look at the definitions of "WAIT" and "FINISHED" states, they look > similar, except for "wait to be reset" in "FINISHED" state . The code really > does not do anything to reset the lcore. It just changes the state to "WAIT". > > > > > From the description above, we can find "FINISHED" is different from > > "WAIT", it > > can shows that lcore has done the work and finished it. Thus, if we remove > > "FINISHED", maybe we will not know whether the lcore finishes its work or > > just > > doesn't start, because this two state has the same tag "WAIT". > Looking at "eal_thread_loop", the worker thread sets the state to "RUNNING" > before sending the ack back to main core. After that it is guaranteed that > the worker will run the assigned function. Only case where it will not run > the assigned function is when the 'write' syscall fails, in which case it > results in a panic.
Quick note: it should not panic. We must find a way to return an error without crashing the whole application. > > Furthermore, consider such a scenario: > > Core 1 need to monitor Core 2 state, if Core 2 finishes one task, Core 1 > > can start > > its working. > > However, if there is only one tag "WAIT", Core 1 maybe start its work at > > the > > wrong time, when Core 2 still does not start its task at state "WAIT". > > This is just my guess, and at present, there is no similar application > > scenario in > > dpdk. > To be able to do this effectively, core 1 needs to observe the state change > from WAIT->RUNNING->FINISHED. This requires that core 1 should be calling > rte_eal_remote_launch and rte_eal_wait_lcore functions. It is not possible to > observe this state transition from a 3rd core (for ex: a worker might go from > RUNNING->FINISHED->WAIT->RUNNING which a 3rd core might not be able to > observe). > > > > > On the other hand, if we decide to remove "FINISHED", please consider the > > following files: > > 1. lib/librte_eal/linux/eal_thread.c: line 31 > > lib/librte_eal/windows/eal_thread.c: line 22 > > lib/librte_eal/freebsd/eal_thread.c: line 31 > I have looked at these lines, they do not capture "why" FINISHED state is > required. > > 2. > > lib/librte_eal/include/rte_launch.h: line 24, 44, 121, 123, 131 3. > > examples/l2fwd- > > keepalive/main.c: line 510 > > rte_eal_wait_lcore(id_core) can be removed. Because the core state has been > > checked as "WAIT", this is a redundant operation
