2.4.18 IDE channels block each other under load?

Can someone tell me what is going on here?

dd if=/dev/zero of=/dev/hda bs=1024 count=1000000

then in another vt:
fdisk /dev/hdc, then immediately press "q".

fdisk "hangs" for a long, long time.
ps -aux says state of dd and fdisk are both "D" strace says fdisk is hanging on the close() /proc/interrupts tell me that ide1 (/dev/hdc) is getting no
int activity for a long, long time. ide0 is very busy.

It is not just dd/fdisk. Any intensive writes on one IDE channel (direct to the hd? device) seem to block any IO on the other device.

Intel SAI2 MB, ServerWorks IDE chipset, 2.4.18, two IDE hard drives /dev/hda and /dev/hdc, 1024MB RAM, RH73 kernel build.

Also seen on Promise PDCx IDE controllers hanging off the PCI.

hdparm settings appear to have no influence on this behavior.

Thanks,
TR.

Are you running DMA on these controllers? It looks like they're running PIO

Can you check the output of 'hdparm /dev/hd_' and "cat /proc/ide/hd_/settings"?

Roy Sigurd Karlsbakk, Datavaktmester

Computers are like air conditioners.
They stop working when you open Windows.

Yes. Baffling. hdparm and prod/ide/hdx both show dma_mode is on.

Normally, I have these running with -X69 (UltraDMA 100)

TR.