Subject: Re: xen/clock.c:get_tsc_offset_ns
To: None <port-xen@NetBSD.org>
From: Jed Davis <email@example.com>
Date: 01/13/2006 02:24:27
YAMAMOTO Takashi <firstname.lastname@example.org> writes:
>> > 2) If so, how much is this breaking?
>> The answer may be "quite a lot", if the shared_info time stuff is
>> updated as infrequently as it sounds like. Also:
> given the overflow and the frequency of today's cpus,
> this function always return a quite small value, compared to NS_PER_TICK.
> so it's effectively just ignored, i think.
More or less; I instrumented the function (to write the value of
tsc_delta into a little ring buffer so I can examine the last 32 from
ddb), and sometimes the delta is a significant fraction of a tick if
there's disk I/O going on. The overall magnitude, I think, might be
enough to cause slight drift (I'm still a little unclear on the
workings of cc_microtime), but it's not the problem I'm actually
having, more on which in a moment.
(let ((C call-with-current-continuation)) (apply (lambda (x y) (x y)) (map
((lambda (r) ((C C) (lambda (s) (r (lambda l (apply (s s) l)))))) (lambda
(f) (lambda (l) (if (null? l) C (lambda (k) (display (car l)) ((f (cdr l))
(C k))))))) '((#\J #\d #\D #\v #\s) (#\e #\space #\a #\i #\newline)))))