PCI Latency's Improve Jitters!

3 cups of coffee improves my jitters. I wonder if it would affect an SCSI system, which runs more "efficiently" than ATA, I'd also say yes. This informative link might help - http://www.reric.net/linux/pci_latency.html


"PCI latency timers are a mechanism for PCI bus-mastering devices to share the PCI bus fairly. "Fair" in this case means that devices won't use such a large portion of the available PCI bus bandwidth that other devices aren't able to get needed work done.


How this works is that each PCI device that can operate in bus-master mode is required to implement a timer, called the Latency Timer, that limits the time that device can hold the PCI bus. The timer starts when the device gains bus ownership, and counts down at the rate of the PCI clock. When the counter reaches zero, the device is required to release the bus. If no other devices are waiting for bus ownership, it may simply grab the bus again and transfer more data.


If the latency timer is set too low, PCI devices will interrupt their transfers unnecessarily often, hurting performance. If it's set too high, devices that require frequent bus access may overflow their buffers, losing data.


So in theory there's a compromise that can be reached somewhere in between, where all devices can get good performance plus a reasonable guarantee that they will get bus access on a timely basis."

This is from the EnTech (PowerStrip) website's FAQ...


"My graphics card and PCI audio card don't seem to get along. Can the PowerStrip help?

Maybe. Graphics cards can sometimes be too aggressive in holding the bus, causing problems for other bus-master PCI devices, most notably PCI sound cards. Although most PCI BIOSes have an option where you can specify a default PCI latency, many cards ignore or override this setting. The PowerStrip has an undocumented feature that allows you to specify the latency for each device on the PCI bus, individually. There aren't any hard and fast rules on appropriate values (a multiple of 8), but as a general guideline higher values yield better performance at the expense of other devices, while lower values are more appropriate to systems with multiple PCI cards. If you want to experiment with this feature, you'll need to manually edit your pstrip.ini file as there are no visual controls available. An example follows:


[Latency]

Enable=1

001812D2=80


In this example, 001812D2 is the PCI device (0018) and vendor (12D2) ID for a Riva128, which normally has a very high latency of 248, and which the PS reduces to 80. If you don't know the PCI device and vendor ID for a particular card, you can find out by checking the PS's hardware details screen, which is opened by clicking the [...] button on the Windows page of the PS Graphics System Information dialog box."


Hope some of ya'll find this exerpt helpful...

Thanks for the info!


The link to the article by the Gentoo CEO is quite helpful also!


Since we obviouslt can't change the PCI Latency in the bios does anyone know of another way besides PStrip?


I just don't like using PStrip because I can use that 10mb it uses as a background process elsewhere! Im not sure if you need to keep the background proccess running after changing the Latency's or not!


Maybe I'll hit up Pstrip and find out!


Cheers