RELENG_7: interrupt eating whole cpu core

[Carlos A. M. dos Santos]

On Feb 6, 2008 5:45 PM, Dominic Fandrey <kamikaze at bsdforen.de> wrote:
> Chuck Swiger wrote:
> > Hi, Dominic--
> >
> > On Feb 6, 2008, at 11:12 AM, Dominic Fandrey wrote:
> >>> behaviour has changed. This is an HP 6510b GR695EA#ABD, if anyone
> >>> thinks it might be helpful, I can supply you with a dmesg and the
> >>> output of pciconf -lv.
> >>
> >> The problem remains with fresh sources:
> >>
> >>  PID USERNAME   THR PRI NICE   SIZE    RES STATE  C   TIME    CPU COMMAND
> >>   12 root         1 171 ki31     0K    16K RUN    0  22:04 97.85%
> >> idle: cpu0
> >>   37 root         1 -64    -     0K    16K CPU1   1   2:35 96.00%
> >> irq14: ata0
> >>   11 root         1 171 ki31     0K    16K RUN    1  19:32  6.40%
> >> idle: cpu1
> >>
> >> The rip is done by k3b, so the drive is accessed through the cam
> >> interface.
> >
> > What are the values being reported by "sysctl hw.ata"?  If you're going
> > to be burning CD/DVDs, you really want to make sure hw.ata.atapi_dma is on.
>
> I cannot believe it was so trivial. The sysctl looks all right.
>
> # sysctl hw.ata                                      0 /root
> hw.ata.wc: 1
> hw.ata.atapi_dma: 1
> hw.ata.ata_dma: 1
>
> But further research revealed:
> # atacontrol mode acd0                               0 /root
> current mode = PIO4
>
> # atacontrol mode acd0 udma33                        0 /root
>
> changed the load dramatically:
>   PID USERNAME    THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
>    12 root          1 171 ki31     0K    16K RUN    0  52:54 100.00% idle: cpu0
>    11 root          1 171 ki31     0K    16K CPU1   1  23:36 94.29% idle: cpu1
> 1087 kamikaze      3  -8    0   133M 36168K physrd 1   1:09  3.17% k3b
>    37 root          1 -64    -     0K    16K WAIT   1  30:10  0.00% irq14: ata0
>
>
> Thank you very much! I used to think that UDMA33 was the default for
> CD-/DVD-Rom drives. I suppose I should review the BIOS settings or change
> something in the hints file.

Wow, now I'm *really* surprised. I used to think that putting

     hw.ata.ata_dma="1"
     hw.ata.atapi_dma="1"

in /boot/loader.conf would be enough to enable DMA mode. In fact I'm
pretty sure it used to be in previous versions of FreeBSD. I created a
/etc/rc.local containing

     #!/bin/sh -
     atacontrol mode acd0 udma33

Two questions, now:

1. Is this related to using atapicam?

2. Should this be considered a bug?

-- 
Carlos A. M. dos Santos