On 03/17/13 18:36, Alan Stern wrote:
On Sun, 17 Mar 2013, Soeren Moch wrote:
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 <smoch@xxxxxx>
--- linux-3.9.0-rc3-guru/drivers/usb/host/ehci-sched.c.orig 2013-03-21 17:36:21.000000000 +0100
+++ linux-3.9.0-rc3-guru/drivers/usb/host/ehci-sched.c 2013-03-21 17:38:56.000000000 +0100
@@ -1214,6 +1214,7 @@ itd_urb_transaction (
memset (itd, 0, sizeof *itd);
itd->itd_dma = itd_dma;
+ itd->frame = -1;
list_add (&itd->itd_list, &sched->td_list);
}
spin_unlock_irqrestore (&ehci->lock, flags);
@@ -1915,6 +1916,7 @@ sitd_urb_transaction (
memset (sitd, 0, sizeof *sitd);
sitd->sitd_dma = sitd_dma;
+ sitd->frame = -1;
list_add (&sitd->sitd_list, &iso_sched->td_list);
}
