kern/81807: Silo overflows with serial multiport cards
Bruce Evans
bde at zeta.org.au
Sat Jun 4 11:44:18 GMT 2005
On Thu, 2 Jun 2005, Bernd Luevelsmeyer wrote:
>> Description:
> The machine has 3 serial 8-port-cards installed, 2 of them ISA cards
> and one PCI card. The card model of all 3 of them is Moxa SmartIO
> C168H (http://www.moxa.com/Product/C168H.htm and
> http://www.moxa.com/Product/C168HPCI.htm). Since Upgrading to
> 5-Stable the ISA cards have high numbers of silo overflows. This did
> not happen with 4-Stable.
> The overflows happened with SCHED_4BSD or SCHED_ULE, with and
> without PREEMPTION in the kernel, and regardless of baudrate (I
> tried 9600 and 115200). Also I tried several HZ values in the kernel
> (100, 1000 and 4000), and it didn't matter.
>
> The machine is a PII with 300 MHz. Now this isn't the most powerful
> (and ISA is a little bit old-fashioned), but the effect happens also
> when only one of the 24 ports is used and it's at 9600 Baud, and
> anyway with 4-Stable there was no problem at all.
Interrupt handling is bad in -current but not usually that bad. The
loss of performance was in the 5-10% range when I tested it a lot on
a 366 MHz Celeron 12-18 months ago. Latency increase is worse than
performance decrease but wasn't noticeable with <= 8 ports at 115200.
> Here is the machine's dmesg:
Everything seems to be set up correctly. sio even handles the isa
ports better that the pci ports. I would have expected silo overflows
to occur for the pci ports first because fast interrupts are not used
for them (try using the PUC_FASTINTR option to fix this). Interrupts
seem to be working at probe time. Do they work later? Use vmstat
or systat -v to check that some keep occurring. Check that fast
interrupts are used by booting with -v.
Bruce
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