Re: [dpdk-dev] [RFC 0/5] Use correct memory ordering in eal functions

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> > rte_eal_remote_launch and rte_eal_wait_lcore need to provide correct
> > memory ordering to address the data communication from main core to
> > worker core and vice versa.
> >
> > There are 2 use cases:
> > 1) All the store operations (meant for worker) by main core should be
> > visible to worker core before the worker core runs the assigned
> > function
> >
> > 2) All the store operations by the worker core should be visible to
> > the main core after rte_eal_wait_lcore returns.
> >
> > For the data that needs to be communicated to the worker after the
> > rte_eal_remote_launch returns, load-acquire and store-release
> > semantics should be used (just like any other writer-reader use case).
> >
> > For the main to worker communication, the pointer to function to
> > execute is used as the guard variable. Hence, resetting of the
> > function pointer is important.
> >
> > For the worker to main communication, the existing code uses the lcore
> > state as the guard variable. However, it looks like the FINISHED state
> > is not really required. Hence the FINISHED state is removed before
> > using the state as the guard variable. I would like some feedback on
> > why the FINISHED state is required. I have not paid attention to what
> > it means for backward compatibility.
> > If it is decided to remove this state, documentation changes are
> > required.
> >
> 
> 
> Most likely all use of volatile in DPDK is suspect.
> Perhaps we should re-enable the "volatile considered harmful" warning in
> checkpatch
Agree.