On Thu, Mar 05, 2015 at 07:56:59AM -0800, Paul E. McKenney wrote: > On Thu, Mar 05, 2015 at 04:35:09PM +0100, Frederic Weisbecker wrote: > > So, in the case we are calling that right after setting cputimer->running, > > I guess we are fine > > because we just updated cputimer with the freshest values. > > > > But if we are reading this a while after, say several ticks further, there > > is a chance that > > we read stale values since we don't lock anymore. > > > > I don't know if it matters or not, I guess it depends how stale it can be > > and how much precision > > we expect from posix cpu timers. It probably doesn't matter. > > > > But just in case, atomic64_read_return(&cputimer->utime, 0) would make sure > > we get the freshest > > value because it performs a full barrier, at the cost of more overhead of > > course. > > Well, if we are running within a guest OS, we might be delayed at any point > for quite some time. Even with interrupts disabled.
You mean delayed because of the overhead of atomic_add_return() or the stale value of cptimer-> fields? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
