On Thu, Mar 21, 2013 at 06:04:59PM +0100, Soeren Moch wrote:

On 03/17/13 18:36, Alan Stern wrote:

quoted

On Sun, 17 Mar 2013, Soeren Moch wrote:

quoted

For each device only one isochronous endpoint is used (EP IN4, 1x 940
Bytes, Interval 1).
When the ENOMEM error occurs, a huge number of iTDs is in the free_list
of one stream. This number is much higher than the 2*M entries, which
should be there according to your description.

Okay, but how did they get there?  With each URB requiring 9 iTDs, and
about 5 URBs active at any time, there should be about 5*9 = 45 iTDs in
use and 2*9 = 18 iTDs on the free list.  By the time each URB
completes, it should have released all 9 iTDs back to the free list,
and each time an URB is submitted, it should be able to acquire all 9
of the iTDs that it needs from the free list -- it shouldn't have to
allocate any from the DMA pool.

Looks like you'll have to investigate what's going on inside
itd_urb_transaction().  Print out some useful information whenever the
size of stream->free_list is above 50, such as the value of num_itds,
how many of the loop iterations could get an iTD from the free list,
and the value of itd->frame in the case where the "goto alloc_itd"
statement is followed.

It might be a good idea also to print out the size of the free list in
itd_complete(), where it calls ehci_urb_done(), and include the value
of ehci->now_frame.

Now I found out what is going on here:

In itd_urb_transaction() we allocate 9 iTDs for each URB with
number_of_packets == 64 in my case. The iTDs are added to
sched->td_list. For a frame-aligned scheduling we need 8 iTDs, the
9th one is released back to the front of the streams free_list in
iso_sched_free(). This iTD was cleared after allocation and has a
frame number of 0 now. So for each allocation when now_frame == 0 we
allocate from the dma_pool, not from the free_list. The attached
patch invalidates the frame number in each iTD before it is sent to
the scheduler. This fixes the problem without the need to iterate
over a iTD list.

Signed-off-by: Soeren Moch <redacted>

Wow!  Great work Soeren!  Talk about a long road to a small fix.  Thanks
for keeping after it.

thx,

Jason.