On Wed, Oct 8, 2014 at 9:00 AM, Stanislaw Gruszka <sgruszka@xxxxxxxxxx> wrote: > > On Wed, Oct 08, 2014 at 07:46:33AM -0400, Mark Asselstine wrote: > > > If rt2x00 does not remove the alignment from the frame before giving it back > > > to mac80211 and the same frame comes into rt2x00 again it should be correctly > > > aligned and no additional header space is required. So this should be fine. > > > > Then I would say this definitely hints at a design flaw in > > rt2x00queue_insert_l2pad(). Take the following scenario. > > > > * skb's first arrival in rt2x00queue_insert_l2pad(), 3 bytes needed > > for frame alignment, 2 bytes for l2pad results in 3 bytes of headroom > > taken. > Not quite realistic assumption - header length will have to be odd then. > > But if such situation would happen we will have: > > header_align=2, payload_align=3, l2pad=3 > > Since payload_align will be bigger than header_align, header_align will > be increased to 6. > > Header will be moved by 6 bytes, frame will be moved by 3 bytes, > between header and frame there will be l2pad equal to 3. > > > * rt2x00lib_txdone() returns 2 bytes of headroom > Return 3 bytes. > > > * skb's second arrival in rt2x00queue_insert_l2pad(), 0 bytes needed > > for frame alignment, 2 bytes for l2pad results in 4 bytes of headroom > > taken. > Header will be moved by 3 bytes. > > > * rt2x00lib_txdone() returns 2 bytes of headroom > Return 3 bytes. > > > Basically as long as any bytes are required for l2pad the headroom > > will lose 4 bytes again and again, never being returned by > > rt2x00lib_txdone(). > > I think that's not true - you made a few mistakes in your scenario, > but perhaps I'm wrong :-) No just me being an idiot. I had thought frame == header + l2pad + payload not frame == payload With this straight your numbers makes sense and my scenario is incorrect. We don't continue to eat in to the headroom but rather take and return a small bit. Thanks for your patience, it has been a while since I have been working on this stuff. I am still motivated to hunt this issue down, you might just need to correct me along the way. Mark > > Stanislaw -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
