Recent Problems with RELENG_7 i386

bf bf2006a at
Wed Oct 8 22:00:33 PDT 2008

--- On Wed, 10/8/08, Jeremy Chadwick <koitsu at> wrote:

> From: Jeremy Chadwick <koitsu at>
> Subject: Re: Recent Problems with RELENG_7 i386
> To: "bf" <bf2006a at>
> Cc: freebsd-stable at
> Date: Wednesday, October 8, 2008, 2:36 PM
> On Wed, Oct 08, 2008 at 10:19:47AM -0700, bf wrote:
> > After updating to RELENG_7 i386 of this weekend, I
> have been having problems
> > with my machine.  When booting normally, the system
> slows or hangs at the
> > login prompt.  If I am able to continue past the
> prompt, I sometimes experience 
> > erratic mouse behavior, and a subsequent hang, after
> varying lengths of time,
> > even under light workloads.  The same problem does not
> seem to occur in 
> > single-user mode, and did not occur with the RELENG_7
> i386 of just over a
> > week ago.  I have been unable to obtain crashdumps so
> far, and the only
> > log messages I can find that weren't present
> before are notices like those
> > recorded below:
> > 
> > Oct  8 11:00:40 myhost kernel: t_delta
> 15.fd80bdcb75b60200 too short
> This comes from src/sys/kern/kern_tc.c, around line 908. 
> I'm not
> familiar with the kernel, but two ideas come to mind:
> 1) If you have Intel SpeedStep (EIST) or AMD
> Cool'n'Quiet enabled in
> your BIOS, try disabling it,
> 2) If you're using powerd, disable it (I don't see
> it enabled),
> 3) Try keeping HZ at 1000 (the default).

Thanks, Jeremy, for taking the time to consider my question and reply.

My CPU is pre-Cool'n'Quiet, and as far as I can tell I had disabled
all forms of power management that may affect the clock speeds.  I have
found that by raising kern.hz to 250, or by using the default, I no
longer receive the t_delta is too short messages, and the other problems
are no longer apparent.  My question is: why did this occur now?  I have
been using a similar configuration for months now without any apparent
problems. My original goal in using a lower kern.hz was to avoid 
burdening my machine with excessive context switching.  I saw the relevant
section of kern_tc.c before I wrote my first message, but when skimming
through the changes in RELENG_7 over the past week or two, I couldn't see
any commit that may have directly affected kernel timekeeping.  Has some
new workload been imposed on the system by recent changes, that may have
made a kern.hz of 100 insufficient?  Is this tuneable setting properly
implemented, so that all parts of the base system are using it's current
value rather than the default?  Could some of my hardware, such as my RTC,
be malfunctioning?


> -- 
> | Jeremy Chadwick                                jdc at
> |
> | Parodius Networking                      
> |
> | UNIX Systems Administrator                  Mountain
> View, CA, USA |
> | Making life hard for others since 1977.              PGP:
> 4BD6C0CB |


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