On Mon, Apr 15, 2013 at 09:37:30PM +0200, Pawel Jakub Dawidek wrote: > On Mon, Apr 15, 2013 at 10:18:15PM +0300, Konstantin Belousov wrote: > > On Mon, Apr 15, 2013 at 08:42:03PM +0200, Pawel Jakub Dawidek wrote: > > > On a mostly unrelated note when two threads (T0 and T1) call get*time() > > > on two different cores, but T0 does that a bit earlier is it possible > > > that T0 can get later time than T1? > > > > Define earlier first. > > > > If you have taken sufficient measures to prevent preemption and > > interruption, > > e.g. by entering spinlock before the fragment that calls get*, then no, > > it is impossible, at least not with any x86 timekeeping hardware we use. > > > > On the other hand, if interrupts are allowed, all bets are off. > > So if we consider only one thread, it is not possible for it to obtain > time t0, be scheduled to different CPU and obtain t1 where t1 < t0?
Yes, I believe this scenario is also not possible. The context switching ensures that thread's view on the global memory is consistent. At least it is so on x86, and I think it must be the same on all other architectures. Otherwise the compiler emited code would not work.
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