Messages in this thread |  | | Date | Tue, 27 Aug 2002 00:49:47 +0200 | From | Andrea Arcangeli <> | Subject | Re: [PATCH] tsc-disable_B9 |
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On Mon, Aug 26, 2002 at 11:45:36AM -0700, Martin J. Bligh wrote: > >> And following your argument that these apps have been silenty broken > >> since 1999, if there's no broken app out there, nobody will ever get the > >> instruction fault. If there's any app broken out there we probably like > > > > No. rdtsc is still usefull if you are clever and statistically filter > > out. Also rdtsc provides you number of cycles, so if you want to know > > how many cycles mov %eax,%ebx takes, you can do that even on > > speedstep. Anything that correlates rdtsc to real time is broken, however. > > It's not correlating it to real time that's the problem. It's getting resceduled > inbetween calls that hurts. Take your example. > > rdtsc > mov %eax,%ebx > <- get rescheduled here > rdtsc > > Broken. May even take negative "time".
you need to save %edx too, then it would be perfectly safe on a synchronized TSC hardware (as far as the reschedule doesn't take more than 2^64 ticks).
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