Re: [PATCH V2 00/11] Live update: cpr-exec

[Peter Xu]

On Mon, Jul 22, 2024 at 10:59:47AM +0200, David Hildenbrand wrote:
> > So I wonder whether there's comparison between exec() and transfer mode
> > that you recently proposed.
> > 
> > I'm asking because exec() (besides all the rest of things that I dislike on
> > it in this approach..) should be simply slower, logically, due to the
> > serialized operation to (1) tearing down the old mm, (2) reload the new
> > ELF, then (3) runs through the QEMU init process.
> > 
> > If with a generic migration solution, the dest QEMU can start running (2+3)
> > concurrently without even need to run (1).
> 
> I'll note (not sure if already discussed) that with the "async-teardown"
> option we have a way to move the MM teardown to a separate process, such
> that it will happen asynchronously.

I just had a look, maybe it won't trivially work, as it relies on QEMU
process to quit first..

async_teardown_fn():
    if (the_ppid == getppid()) {
        pause();
    }

While if we stick with exec(), then PID shouldn't change, so the teardown
process can hold the mm and pause until the VM is destroyed..

Thanks,

-- 
Peter Xu