Re: too short/too long (sys/kern_tc.c)

On 02/27/07 11:34, Poul-Henning Kamp wrote:
In message <45E43984.4020809@xxxxxxxxxxx>, Eric Anderson writes:

When I boot a -CURRENT box with boot verbose enabled inside qemu, I see
one of these messages about every second:

15.f68c5ee76faebe10 too short
16.0f822e13092c5580 too long

This is a symptom of lousy scheduling or even worse interrupt
latency.

In your case +0.060/-0.036 sec per 16 seconds or a couple of percent
in relative terms. (The printf is counter intuitive: the integer
part is in decimal).

I will readily admit that the 1/256 of a second limit is chosen
pretty much at random, but with an eye to allowing a division
by 16 to get close the right result.

All of this futz is of course to avoid floating point in the kernel.

As to why: My main suspect would be the BIOS/ACPI/SMM code, with
a keen eye to the new interrupt filtering code and what it might
do to the clock/scheduling interrupts.


Thanks for the reply and info. It turns out that enabling acpi in the kernel makes it go away, so I'm happy. I'm not certain if anyone should care much about it, besides the fact that it might be pointing to something else more important.


Are these at all related to the calcru messages people have been seeing? I have to admit, I haven't looked much in the archives on the calcru history. I'm mostly asking for the others who have responded to me privately after sending this message.


Eric

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