> >Flexers might find the DPC Latency checker of use. You can download it >free at the Thesycon site under "Free Utilities" >
EXCELLENT suggestion, Mike, thanks! I know Udo Eberhardt (who runs the company that wrote this tool), and I wasn't even aware of this utility. So, thanks very much! Interpreting the results can be tricky, even if you're a Windows driver developer. Keep in mind the tool reports ISR to DPC latency... not device interrupt request to ISR latency. ISR to DPC latency is best thought of as the time it takes from a device's interrupt being serviced to when that device is able to start returning data to an application. This is typically the type of latency that really matters to device in a Windows system. Note that the AVERAGE ISR to DPC latency is almost never a problem. Rather, what you're looking for is the repeated occurrence of "outliers"... worst-case ISR to DPC latency. The bad part of all this is if you experience packet loss as a result of excessive worst-case (or even average) ISR to DPC latency, there's often little you can do about it. You're mostly restricted to changing the devices involved... and it's rarely the device you're concerned about that's the problem. I knew of an infamous network card that created well over 1ms of ISR to DPC latency (for other drivers in the system) each time it periodically checked the speed of the network to which it was connected. Devices that were "backed up" behind this NIC often suffered from overruns and dropped data. Swap the NIC, and problems with those other devices disappeared. The worst offenders, in terms of causing excessive ISR to DPC latency for other system devices, are typically video and network cards. Thanks again, Mike, for making us all aware of this tool, de Peter K1PGV _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
