vmstat questions

[Dan Nelson]

In the last episode (Jun 01), Morgan Wesström said:
> Hi. This is my "vmstat -i" from my newly installed 7.2-RELEASE-amd64:
> 
> # vmstat -i
> interrupt                          total       rate
> irq4: sio0                          1105          0
> irq17: em1 uhci1+               10921807        182
> irq19: uhci3++                   8196905        136
> cpu0: timer                    117164643       1956
> irq256: em0                      7346687        122
> irq257: re0                       166625          2
> cpu1: timer                    117164471       1956
> Total                          260962243       4358
> 
> For a long time I've tried to find out what the + and ++ means. Can
> anyone shed some light on that?
> 
> Also, where did my atapcis on irq19 go? I'm pretty sure I had them
> listed there in 7.0-RELEASE.

There is a very small buffer in the kernel for recording which devices are
assigned to which IRQs in a human-readable format (MAXCOMLEN: 19 characters
per IRQ, including the "irqNNN:" text).  Code in
/sys/kern/kern_intr.c:intr_event_update() truncates the list and adds a +
for each omitted device name.

http://fxr.watson.org/fxr/source/kern/kern_intr.c#L194

I'm not even sure why MAXCOMLEN is being used at this point; it's not
storing a command name.

http://fxr.watson.org/fxr/source/sys/interrupt.h#L104

I don't know what the repercussions would be if you increased MAXCOMLEN to
40, but you can try bumping it and see what breaks :)


-- 
	Dan Nelson
	dnelson at allantgroup.com