Re: [PATCH] USB: EHCI: fix for leaking isochronous data

From: Alan Stern
Date: Thu Mar 21 2013 - 17:12:09 EST

On Thu, 21 Mar 2013, Alan Stern wrote:

> On Thu, 21 Mar 2013, Soeren Moch wrote:
> > 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.
> Okay, that is a problem. But it shouldn't be such a big problem,
> because now_frame should not be equal to 0 very often.

Oh, wait, now I get it. We never reach a steady state, because the
free list never shrinks, but occasionally it does increase when
now_frame is equal to 0. Even though that doesn't happen very often,
the effects add up.

Very good; tomorrow I will send your patch in.

Alan Stern

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at