On Tuesday 20 February 2007 12:27 pm, [EMAIL PROTECTED] wrote: > > This patch turns off periodic list processing in the EHCI controller for > the duration of processor frequency changes.
Did you test this with any kind of isochronous device active, like a set of USB speakers playing? ISO transfers work differently than the interrupt transfers you tested (with a HID device). Also ... what kind of hardware did you test this with? I wonder how much of the (potential) 1.125 msec it was spinning while waiting for the periodic schedule to actually turn off. That seems like it should be modifying the latency metrics used by cpufreq... is there even a feedback mechanism whereby the system can say that _right now_ it would take this much more time? Last time I remember looking at cpufreq, it had static metrics basically relating only to the CPUs; so costs related to components like EHCI were hidden. (Much less costs associated with re-clocking other peripherals, which is a big issue with embedded SOC chips!) The patch looks mostly OK, but the issue with isochronous transfers is a difference in how transfer completion is handled in the hardware. Rather than scanning a queue head node in the schedule tree, which will be re-scanned after the periodic list is re-activated. Instead, isochronous transfers use an entirely different hardware mechanism. Their ITDs go before that schedule tree, and won't get re-scanned after the relevant frame passes. I'd not be sure that the current iso scanning logic would behave correctly with this kind of on/off mechanism. In fact I'd kind of expect it to break. That's in addition to the issue that it might not be a Good Thing to let cpufreq create audio (or video etc) dropouts ... Maybe the best solution to this issue would be to reject the cpufreq change if ISO transfers are active on EHCI. - Dave ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
