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Message-ID: <20130314092511.GA29105@openwall.com>
Date: Thu, 14 Mar 2013 13:25:11 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: clock err in timers (alarm, status ...) and fix
On Thu, Mar 14, 2013 at 10:08:46AM +0100, magnum wrote:
> Solar, any comments?
I haven't looked into this closely, but from Costin's posting it sounds
like in jumbo you've misused timer ticks to implement jumbo's timeout
feature. The timer ticks should not be used to measure prolonged
periods of time where we care about precision.
As to the 10 vs. 8 seconds discrepancy Costin observed, my guess is that
he may be using a build with emulated timers (OS_TIMER is off, which it
is on AMD GPU enabled builds and on Windows). With OS-provided timer
ticks, I'd expect the imprecision to be a lot less than that (but still
not good enough for the timeout feature).
Core (aka "official JtR") only uses the timers for things where
precision is not crucial. The worst, in terms of requiring some sort of
precision, is the "Save = ..." setting in john.conf (how frequently to
update the pot/rec/log files). Yes, it may be off by up to a factor of
two on non-OS_TIMER builds. This is somewhat nasty, but I'm not sure if
we care to address it.
Alexander
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