On 8.7.2021 11.43, Ikjoon Jang wrote:
> When unlinked urbs are queued to the cancelled td list, many tds
> might be located after hw dequeue pointer and just marked as no-op
> but not reclaimed to num_trbs_free. This bias can leads to unnecessary
> ring expansions and leaks in atomic pool.
Good point, in that case trbs turned no-op never get added to free trb count.
>
> To prevent this bias, this patch counts free TRBs every time xhci moves
> dequeue pointer. This patch utilizes existing
> update_ring_for_set_deq_completion() function, renamed it to move_deq().
>
> When it walks through to the new dequeue pointer, it also counts
> free TRBs manually. This patch adds a fast path for the most cases
> where the new dequeue pointer is still in the current segment.
>
This looks like an option.
Another approach would be to keep the normal case fast, and the special case code simple.
Something like:
finish_td()
...
/* Update ring dequeue pointer */
if (ep_ring->dequeue == td->first_trb) {
ep_ring->dequeue = td->last_trb;
ep_ring->deq_seg = td->last_trb_seg;
ep_ring->num_trbs_free += td->num_trbs - 1;
inc_deq(xhci, ep_ring);
} else {
move_deq(...);
}
move_deq(...)
{
while(ring->dequeue != new_dequeue)
inc_deq(ring);
inc_deq(ring);
}
inc_deq() increases the num_trbs_free count.
I haven't looked at the details of this yet, but I'm away for the next two weeks so
I wanted to share this first anyway.
-Mathias
