MILO> SET PCI_LATENCY nn
where nn is any value from 0 to 255. So, what does this command do? In
short it sets the PCI latency of all of the PCI bus master devices in the
system and, if the system supports environment variables, it will do it
each time the system boots. The PCI latency (in this context) is the
amount of time (in PCI clock cycles) that a device will hang onto the
PCI bus. In other words, the higher the latency the greater the amount
of data transfered each time that a PCI device gets hold of the PCI bus.
I have set the default to 32 (which is also WNT ARC and the SRM's default
value) but I have experimented with 255. My current system is using 255 and
has run with no problems at all; it is faster (I guess that the SCSI and
video are running faster as they are transfering more data each time they
transfer). Hold on though, I hear you say, there *must* be a drawback, well
there is. The maximum time that a PCI master device has to wait for the
bus is N*Latency and the higher the latency, the longer the maximum potential
wait. This could degrade performance in a multi-master system where many
masters are trying to get hold of the PCI bus. This is why I have made it
settable; your milage may vary. I don't believe that there are any data
corruption implications, I certainly have seen none.
The sources are V2.0/src/milo-2.0.28-(ELF).tar.gz and they build
against the stock 2.0.28 sources + David M-T's 2.0.21 patches. I haven't
updated the 2.1.* sources as I am behind and my 2.1.* MILO sources are in
a complete mess (I decided to reorganise them a little).
Dave
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David A Rusling Principal Engineer
European Semiconductor Applications Digital Equipment Co Ltd.,
Engineering PO Box 121,
Imperial Way,
Worton Grange
Reading RG2 0TU
Linux, Alpha, StrongArm, PCI Tel: UK-(0)1734-204380
Fax: UK-(0)1734-203133
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