I trust you won't mind if I put this on the public mailing list. In general, problems of this sort should be discussed in public. In addition to creating a permanent record in the various mailing list archives, it also gives other people a chance to learn about these problems and to chime in if they think of something I have overlooked. On Wed, 20 Feb 2013, Soeren Moch wrote: > Ok. I use 2 em2840-based usb sticks (em28xx driver) attached to a > Marvell Kirkwood-SoC with a orion-ehci usb controller. These usb sticks > stream dvb data (digital TV) employing isochronous usb transfers (user > application is vdr). > > Starting from linux-3.6 I see > ERROR: 1024 KiB atomic DMA coherent pool is too small! > in the syslog after several 10 minutes (sometimes hours) of streaming > and then streaming stops. > > In linux-3.6 the memory management for the arm architecture was changed, > so that atomic coherent dma allocations are served from a special pool. > This pool gets exhausted. The only user of this pool (in my test) is > orion-ehci. Although I have only 10 URBs in flight (5 for each stick, > resubmitted in the completion handler), I have 256 atomic coherent > allocations (memory from the pool is allocated in pages) from orion-ehci > when I see this error. So I think there must be a memory leak (memory > allocated atomic somewhere below the usb_submit_urb call in em28xx-core.c). > > With other dvb sticks using usb bulk transfers I never see this error. > > Since you already found a memory leak in the ehci driver for isoc > transfers, I hoped you can help to solve this problem. If there are > additional questions, please ask. If there is something I can test, I > would be glad to do so. I guess the first thing is to get a dmesg log showing the problem. You should build a kernel with CONFIG_USB_DEBUG enabled and post the part of the dmesg output starting from when you plug in the troublesome DVB stick. It also might help to have a record of all the isochronous-related coherent allocations and deallocations done by the ehci-hcd driver. Are you comfortable making your own debugging changes? The allocations are done by a call to dma_pool_alloc() in drivers/usb/host/ehci-sched.c:itd_urb_transaction() if the device runs at high speed and sitd_urb_transaction() if the device runs at full speed. The deallocations are done by calls to dma_pool_free() in ehci-timer.c:end_free_itds(). 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
