Return-path: Received: from arrakis.dune.hu ([78.24.191.176]:54754 "EHLO arrakis.dune.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750781AbcBHLEM (ORCPT ); Mon, 8 Feb 2016 06:04:12 -0500 Subject: Re: [RFC v4] mac80211: add A-MSDU tx support To: Krishna Chaitanya , Emmanuel Grumbach References: <1454920723-48071-1-git-send-email-nbd@openwrt.org> Cc: linux-wireless , Johannes Berg From: Felix Fietkau Message-ID: <56B87625.6040206@openwrt.org> (sfid-20160208_120415_490028_DFBBC240) Date: Mon, 8 Feb 2016 12:04:05 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 2016-02-08 10:54, Krishna Chaitanya wrote: > On Mon, Feb 8, 2016 at 2:56 PM, Emmanuel Grumbach wrote: >> On Mon, Feb 8, 2016 at 10:38 AM, Felix Fietkau wrote: >>> Requires software tx queueing support. frag_list support (for zero-copy) >>> is optional. >>> >>> Signed-off-by: Felix Fietkau >>> --- >> >> >> Ok - looks fine, but... and here comes the hard stuff. >> The frame size in the PLCP is limited in a way that you can't - from a >> spec POV - enable A-MSDU for low rates. Of course, you don't want to >> do that for low rates at all regardless of the spec. >> Since you build the A-MSDU in the mac80211 Tx queue which is not aware >> of the link quality, how do we prevent A-MSDU if the rate is low / >> dropping. >> I'd even argue that when the rates get lower, you'll have more >> packets piling up in the software queue and ... even more chance to >> get A-MSDU in the exact case where you really want to avoid it? > > Similar to triggering AMPDU setup, we should put this control > in RC (minstrel) to start/stop AMSDU based on link quality/if the rates > drop below a pre-defined MCS (or) only for best-throughput rates. I think starting/stopping A-MSDU based on the rate is a bad idea. Even with low rates, using A-MSDU can be a good thing (especially for TCP ACKs), it just needs different size limits. - Felix