On Wed, 2005-08-03 at 09:10 -0700, Christoph Lameter wrote:
> On Wed, 3 Aug 2005, Alex Williamson wrote:
>
> > be a reasonable performance vs absolute accuracy trade-off. What
> > happens to your worst case time if you (just for a test) hard code a
> > min_delta of something around 20-50? There could be some kind of
>
> Think about a threaded process that gets time on multiple processors
> and then compares the times. This means that the time value obtained later
> on one thread may indicate a time earlier than that obtained on another
> thread. An essential requirement for time values is that they are
> monotonically increasing. You are changing that basic nature.
Ok, I can see the scenario where that could produce jitter. However,
that implies than any exit through that path could produce jitter as it
is. For instance:
CPU0 CPU1
read lcycle
read itc
read lcycle
read itc
cmpxchg
oops, lcycle is stale
So the window already exists for this...
Alex
--
Alex Williamson HP Linux & Open Source Lab
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