On Tue, 15 Jan 2008, Mathieu Desnoyers wrote: > > Ok, but what actually insures that the clock->cycle_* reads won't be > reordered across the clocksource_read() ?
<looks at code> Hmm, interesting.I didn't notice that clocksource_read() is a static inline. I was thinking that since it was passing a pointer to a function, gcc could not assume that it could move that code across it. But now looking to see that clocksource_read is simply a static inline that does: cs->read(); But still, can gcc assume that it can push loads of unknown origin variables across function calls? So something like: static int *glob; void foo(void) { int x; x = *glob; bar(); if (x != *glob) /* ... */ } I can't see how any compiler could honestly move the loading of the first x after the calling of bar(). With glob pointing to some unknown variable, that may be perfectly fine for bar to modify. > > > > > > > + cycle_raw = clock->cycle_raw; > > > > + cycle_last = clock->cycle_last; > > > > + > > > > + /* read clocksource: */ > > > > + cycle_now = clocksource_read(clock); So the question here is,can cycle_raw and cycle_last be loaded from the unknown source that clock points to after the call to clocksource_read()? I'm thinking not. > > > > + > > > > + /* calculate the delta since the last update_wall_time: > > > > */ > > > > + cycle_delta = (cycle_now - cycle_last) & clock->mask; > > > > + > > > > + } while (cycle_raw != clock->cycle_raw || > > > > + cycle_last != clock->cycle_last); > > > > + > > > > + return cycle_raw + cycle_delta; > > > > +} -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/