On Sun, 10 Mar 2013, Soeren Moch wrote: > > 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. > > Sorry for my late response. Now I built a kernel 3.8.0 with usb_debug > enabled. See below for the syslog of device plug-in. > > > 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(). > > > > I added a debug message to > drivers/usb/host/ehci-sched.c:itd_urb_transaction() to log the > allocation flags, see log below. But it looks like you didn't add a message to end_free_itds(), so we don't know when the memory gets deallocated. And you didn't print out the values of urb, num_itds, and i, or the value of itd (so we can match up allocations against deallocations). > For me this looks like nothing is > allocated atomic here, so this function should not be the root cause of > the dma coherent pool exhaustion. I don't understand. If non-atomic allocations can't exhaust the pool, why do we see these allocations fail? > Are there other allocation functions > which I could track? Yes, but they wouldn't be used for isochronous transfers. See ehci_qtd_alloc(), ehci_qtd_free(), ehci_qh_alloc(), and qh_destroy() in ehci-mem.c, as well as some other one-time-only coherent allocations in that file. 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
