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Message-ID: <4863C86A.4080903@nortel.com>
Date: Thu, 26 Jun 2008 10:48:42 -0600
From: "Chris Friesen" <cfriesen@...tel.com>
To: linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: wacky select timeout behaviour in strace
I've got something odd in a couple of recent strace logs (running on an
older kernel, I haven't yet tried to reproduce in mainline).
First case:
20418 22:06:50.583303 select(19, [7 11 12 13 14 15 16 17 18], NULL,
NULL, {0, 498508}) = 1 (in [11], left {0, 0}) <5.074137>
select() was called with a timeout of half a second. Five seconds later
it returns with zero time left and a single socket readable. Why
wouldn't it have returned after half a second with a timeout?
Second case:
18383 01:46:23.572951 select(16, [15], NULL, NULL, {1, 0}) = 1 (in [15],
left {0, 732000}) <1.337443>
Here we call select with a timeout of 1 sec, then 1.3337 sec later we
return saying that we have 732ms left to sleep.
In addition, there was an interval timer set up to fire every 500ms, and
it didn't interrupt the select call. It did fire 60ms after the select
call returned. Interestingly, the timing of that firing (x.97 sec)
didn't match the normal times (x.07 and x.57), but it then returned to
the normal times after the single abnormal firing.
Anyone have any ideas what's going on? This doesn't appear to be an
strace artifact, as I can reproduce it without tracing the process in
question. It also doesn't appear to be a system-wide artifact as I know
from instrumentation that other tasks are running during this interval.
Thanks,
Chris
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