On August 18, 2016 5:54:49 PM GMT+02:00, Jakub Jelinek <ja...@redhat.com> wrote: >On Thu, Aug 18, 2016 at 08:51:31AM -0700, Andi Kleen wrote: >> > I'd prefer to make updates atomic in multi-threaded applications. >> > The best proxy we have for that is -pthread. >> > >> > Is it slower, most definitely, but odds are we're giving folks >> > garbage data otherwise, which in many ways is even worse. >> >> It will likely be catastrophically slower in some cases. >> >> Catastrophically as in too slow to be usable. >> >> An atomic instruction is a lot more expensive than a single >increment. Also >> they sometimes are really slow depending on the state of the machine. > >Can't we just have thread-local copies of all the counters (perhaps >using >__thread pointer as base) and just atomically merge at thread >termination?
I suggested that as well but of course it'll have its own class of issues (short lived threads, so we need to somehow re-use counters from terminated threads, large number of threads and thus using too much memory for the counters) Richard. > Jakub
