On Wed, Oct 8, 2014 at 3:52 PM, Mark Asselstine <asselsm@xxxxxxxxx> wrote: > 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 > By the way, I assumed that this due to the name and contents of rt2x00queue_align_frame(). Where all the data (header and payload) are aligned to a 4-byte boundary and the function is name 'align_frame'. I assume your interpretation is the correct one, can you confirm? Mark > 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
