On Tue, Oct 04, 2022 at 05:59:36PM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu ([email protected]) wrote: > > To prepare for thread-safety on page accountings, at least below counters > > need to be accessed only atomically, they are: > > > > ram_counters.transferred > > ram_counters.duplicate > > ram_counters.normal > > ram_counters.postcopy_bytes > > > > There are a lot of other counters but they won't be accessed outside > > migration thread, then they're still safe to be accessed without atomic > > ops. > > > > Signed-off-by: Peter Xu <[email protected]> > > I think this is OK; I'm not sure whether the memset 0's of ram_counters > technically need changing.
IMHO they're fine - what we need there should be thing like WRITE_ONCE() just to make sure no register caches (actually atomic_write() is normally implemented with WRITE_ONCE afaik). But I think that's already guaranteed by memset() as the function call does, so we should be 100% safe. > I'd love to put a comment somewhere saying these fields need to be > atomically read, but their qapi defined so I don't think we can. How about I add a comment above ram_counters declarations in ram.c? > > Finally, we probably need to check these are happy on 32 bit builds, > sometimes it's a bit funny with atomic adds. Yeah.. I hope using qatomic_*() APIs can help me avoid any issues. Or anything concerning? I'd be happy to test on specific things if there are. > > > Reviewed-by: Dr. David Alan Gilbert <[email protected]> Thanks! -- Peter Xu
