On Thu, 4 Sep 2014, Christian Melki wrote: > Hi Alan. > > The machine has only two cameras inserted (no hids, nothing else). > While the cameras have an interrupt endpoint, I disabled it in > uvc_video. Still I don't get more than two cameras into the schedule. > So there are no interrupt endpoints besides the one used for the > internal hubs. They are 2 and their schedule is 4bytes per 256ms. > Hardly a large load. The total load isn't what matters; it's more a question of what slots in the schedule get used up. The periodic scheduler in ehci-hcd isn't capable of moving things around if the schedule is fragmented and a large contiguous reservation is needed. > With the interrupt endpoints on the camera, usage was 98%, now it's > 93% with them disabled. With two cameras you get 93% usage? And you wonder why you can't get three cameras to fit in the schedule? > T: Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=480 MxCh= 2 > B: Alloc=744/800 us (93%), #Int= 2, #Iso= 10 > > The only reason I can come up with to make this happen is that the > driver does not send 3 packets per microframe worth of isoc-data or > that the scheduler does not account for that capacity, ie only 8 > microframes * 1024 bytes. Something along that path. Or the scheduler > is really, really broken. :) The scheduler isn't really broken, but it definitely is not as capable as it ought to be. > That would probably give me 80%+ usage when it should not be more > than 30-35%. > > Searching the net for it yields approx. the same information. People > are lucky to be able to run two cameras with Linux. I can't tell what's going on without a lot more detailed information. To start with, I'd need the contents of /sys/kernel/debug/usb/devices for all devices on the bus (not just one or two lines) -- that's while the cameras are both running. And it wouldn't hurt to have the dmesg log for the period when you start using the cameras, with debugging enabled for ehci-hcd. Also, recent kernels (try for 3.16) have more detailed scheduling info in ehci-hcd's debugfs directories. There's a new file named "bandwidth" that would be highly relevant. 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
