On 16.01.2013 18:47, Jason Cooper wrote:

On Wed, Jan 16, 2013 at 06:32:09PM +0100, Soeren Moch wrote:

quoted

On 16.01.2013 09:55, Soeren Moch wrote:

quoted

On 16.01.2013 04:24, Soeren Moch wrote:

quoted

I did not bisect it, but Marek mentioned earlier that commit
e9da6e9905e639b0f842a244bc770b48ad0523e9 in Linux v3.6-rc1 introduced
new code for dma allocations. This is probably the root cause for the
new (mis-)behavior (due to my tests 3.6.0 is not working anymore).

I don't want to say that Mareks patch is wrong, probably it triggers a
bug somewhere else! (in em28xx?)

The em28xx sticks are using isochronous usb transfers. Is there a
special handling for that?

I'm looking at that now.  It looks like the em28xx wants (as a maximum)
655040 bytes (em28xx-core.c:1088).  There are 5 transfer buffers, with
64 max packets and 2047 max packet size (runtime reported max & 0x7ff).

If it actually needs all of that, then the answer may be to just
increase coherent_pool= when using that driver.  I'll keep digging.

I already tested with 4M coherent pool size and could not see
significant improvement. Would it make sense to further increase the
buffer size?

Regards,
Soeren