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
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