linux-kernel - Re: Early hang with 2.6.21-rc4-rt1

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Message-ID: <adavegpl0jd.fsf@cisco.com>
Date:	Sun, 25 Mar 2007 10:01:58 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Early hang with 2.6.21-rc4-rt1

 > I finally got curious enough to want to debug why starting kvm with
 > tun/tap networking produces a bunch of
 > 
 >     rtc: lost some interrupts at 1024Hz.
 > 
 > messages.  So I'm assuming it's a ~millisecond irqs-off section
 > somewhere.

And after everything, it's a heisenbug -- I repeatably get that lost
interrupts message on stock 2.6.21-rc4 but never on -rt1 with
CONFIG_LATENCY_TRACE.

Any suggestion of where to look?  My /proc/latency_trace stays
stubbornly empty -- are there any sysctls I need to change from their
default to get latency tracing?  I'm a complete noob when it comes to
the -rt patch, so I'm not sure what the right way to use the tracing
infrastructure to track down this lost rtc interrupts issue is.

Thanks, 
  Roland
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