Dears, We have apply the patch you mentioned below. the result is the same. And we see the phenomenon about how long the urb will be complete. the time duration may not 20 ms periodically, sometime is about 30 ms. Could you explain the reason about why 20ms is "must" in ehci iso schedule mechanism? And it is possible longer urb complete time in sometimes, right? Thanks a lot! Best Regards, Soho 2011/5/27 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>: > On Thu, 26 May 2011, Soho Soho123 wrote: > >> Dears, >> >> >> Let me ask the question more detail below. >> >> 1. So linux 2.6.30 has bug, "it can work over night" is wrong. > > Yes. > >> 2. the meaning of yours is uvc video driver submit new urb too late, right? >> but as my understand, the new urb is submited when the urb has complete. so, >> the time for urb complete is too long, right? >> the time duration for ehci irq service function to finish is too long, right? >> Or, >> ehci irq service function can not be run due to CPU resource has been >> occupied by other device, right? > > Yes. If you use usbmon (see Documentation/usb/usbmon.txt) you'll see > exactly when each URB is submitted and when it completes. > >> 3. do you have any suggestion for work around ? > > Start with usbmon to make sure my analysis is correct. Then try to > figure out what part of your system is responsible for the high > interrupt latency and fix it. > > Another thing to try is applying commit > 1e12c910eed82da6971f1c0421a069c680faba2e (EHCI: don't rescan interrupt > QHs needlessly) from the USB development tree: > > https://git.kernel.org/?p=linux/kernel/git/gregkh/usb-2.6.git;a=commitdiff;h=1e12c910eed82da6971f1c0421a069c680faba2e > > That was specifically intended to help reduce latency. > > You can also try increasing the number of URBs to 32. But that's not > going to do anything about the source of the problem. > > Alan Stern > > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
