On 22.01.2013 19:13, Arnd Bergmann wrote:
On Monday 21 January 2013, Greg KH wrote:
I don't know a lot about USB, but I always assumed that this was not a normal condition and that there are only a couple of URBs per endpoint used at a time. Maybe Greg or someone else with a USB background can shed some light on this.
There's no restriction on how many URBs a driver can have outstanding at once, and if you have a system with a lot of USB devices running at the same time, there could be lots of URBs in flight depending on the number of host controllers and devices and drivers being used.
I only use one host controller and (in this test) two usb devices with the same driver.
Ok, thanks for clarifying that. I read some more of the em28xx driver, and while it does have a bunch of URBs in flight, there are only five audio and five video URBs that I see simultaneously being submitted, and then resubmitted from their completion handlers. I think this means that there should be 10 URBs active at any given time in this driver, which does not explain why we get 256 allocations.
I think the audio part of the em28xx bridge is not used in my DVB tests.
Are there other allocations from orion-ehci directly? Maybe something special for isochronous transfers (since there is no problem with my other dvb sticks using bulk transfers)?
I also noticed that the initial submissions are all atomic but don't need to, so it may be worth trying the patch below, which should also help in low-memory situations. We could also try moving the resubmission into a workqueue in order to let those be GFP_KERNEL, but I don't think that will help.
I built a linux-3.7.4 with the em28xx patch and both of your dma-mapping.c patches. I still see the ERROR: 1024 KiB atomic DMA coherent pool is too small!
Soeren