Return-path: Received: from mail-wm0-f44.google.com ([74.125.82.44]:34090 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752577AbcCaGjp convert rfc822-to-8bit (ORCPT ); Thu, 31 Mar 2016 02:39:45 -0400 Received: by mail-wm0-f44.google.com with SMTP id p65so210880905wmp.1 for ; Wed, 30 Mar 2016 23:39:39 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <56FBF0A4.5090508@candelatech.com> References: <1458898743-21118-1-git-send-email-michal.kazior@tieto.com> <56FAA518.2000805@candelatech.com> <56FBF0A4.5090508@candelatech.com> Date: Thu, 31 Mar 2016 08:39:38 +0200 Message-ID: (sfid-20160331_083950_438363_DF06B334) Subject: Re: [RFC] ath10k: implement dql for htt tx From: Michal Kazior To: Ben Greear Cc: Dave Taht , "ath10k@lists.infradead.org" , linux-wireless , make-wifi-fast@lists.bufferbloat.net, "codel@lists.bufferbloat.net" Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 30 March 2016 at 17:28, Ben Greear wrote: > On 03/30/2016 02:22 AM, Michal Kazior wrote: >> >> On 29 March 2016 at 17:54, Ben Greear wrote: >>> >>> On 03/29/2016 12:49 AM, Michal Kazior wrote: >>> >>>>> if you are getting a pure codel result of 160ms, that means the >>>>> implementation is broken. But I think (after having read your >>>>> description twice), the baseline result today of 160ms of queuing was >>>>> with a fq_codel *qdisc* doing the work on top of huge buffers, >>>> >>>> >>>> >>>> Yes. The 160ms is with fq_codel qdisc with ath10k doing DQL at 6mbps. >>>> Without DQL ath10k would clog up all tx slots (1424 of them) with >>>> frames. At 6mbps you typically want/need a handful (5-10) of frames to >>>> be queued. >>> >>> >>> >>> Have you actually verified you can use all tx slots? >> >> >> It works in most cases. I guess you're suspecting some of your >> tx(flushing?) problems might be induced by overcommiting? >> >>> The way the >>> firmware uses it's tx buffers I think you may not be able to actually >>> do that...and in practice, you will get a lot fewer usable tx-buffers >>> than configured.... >> >> >> Could be, e.g. I'm aware management frames are kind of a special case >> in recent firmware revisions. >> >> What would/do you expect firmware would/will do when we overcommit? >> The driver does advertise number of HTT tx slots so I would expect it >> to work fine if it didn't crash during boot. > > > The firmware will return something like tx-dropped immediately. The reason > is that the firmware keeps more than one internal priority queue, and in > general, reserves > some of the tx-descriptors for high priority. > > So, you never see tx-queues completely full in the driver, so tx queues are > not stopped farther up the stack. > > Possibly I am confused about some of this, so I'm quite curious if you ever > see > tx-queues determined to be full in the ath10k driver. I haven't analyzed it this much. Nevertheless it's good to know we might be overcommiting on the HTT Tx. One more reason to use DQL and/or schedule tx in a smarter way. Michał