Hi, I am currently looking into the old problem of the mac80211 rate control algorithms and USB devices. The Ralink USB devices (and as far as I know, the other USB devices as well), do not work well with the PID and Minstrel algorithms. This is caused by the fact that USB devices do not report the TX status to mac80211. When the URB callback function is called, it only indicates the frame was uploaded to the hardware, and the frame has been enqueued in the hardware queue within the USB device itself. The statistics about the number of retries and the ACK status are therefor lost. These statistics are however often still available (in a limited form) within the device registers. Although these statistics cannot be obtained per frame, it might still be possible to control a working rate control algorithm with it. My current idea for this, is not to generate a completely new algorithm, but base it on the currently existing rate controls. For this I want to introduce a new flag: IEEE80211_HW_REQUIRES_BATCH_TX_STATUS, This flag will enable polling in mac80211, where the callback function ieee80211_ops->get_tx_stats is called. In this function the driver can fill in a structure containing the number of Acked frames, non-acked frames and retries. This structure can then be passed to a new function in the rate_control_ops structure. The problem here is that we have lost the per-sta statistics. However using the single TX status reports, we can count the number of frames which are sent for a given STA during the poll interval. We can then determine the percentage of frames sent for that STA, We can then add the percentage of the retry and ACK count to each STA. Throughout poll interval the rate algorithm would send all frames to the same STA with the same TX rate, but between polls, the rate will be updated. Overall these changes will not make the optimal use of PID or Minstrel, but it would at least improve the situation for USB. Any thoughts about this solution? Ivo -- 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
