From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.toke.dk ([52.28.52.200]:47247 "EHLO mail.toke.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728127AbeIJTyn (ORCPT ); Mon, 10 Sep 2018 15:54:43 -0400 From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Johannes Berg , linux-wireless@vger.kernel.org, make-wifi-fast@lists.bufferbloat.net Cc: Rajkumar Manoharan , Felix Fietkau Subject: Re: [PATCH RFC v3 1/4] mac80211: Add TXQ scheduling API In-Reply-To: <1536591110.3224.76.camel@sipsolutions.net> References: <153635803319.14170.10011969968767927187.stgit@alrua-x1> <153635897010.14170.2992498632345986102.stgit@alrua-x1> <1536565717.3224.12.camel@sipsolutions.net> <87musplivy.fsf@toke.dk> <1536577419.3224.50.camel@sipsolutions.net> <87zhwpjzme.fsf@toke.dk> <1536583587.3224.71.camel@sipsolutions.net> <87wortjy8n.fsf@toke.dk> <1536585051.3224.72.camel@sipsolutions.net> <87r2i1jxse.fsf@toke.dk> <1536591110.3224.76.camel@sipsolutions.net> Date: Mon, 10 Sep 2018 17:00:11 +0200 Message-ID: <87muspjt38.fsf@toke.dk> (sfid-20180910_170019_192210_479CD83B) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: Johannes Berg writes: > On Mon, 2018-09-10 at 15:18 +0200, Toke H=C3=B8iland-J=C3=B8rgensen wrote: > >> If we have the start_schedule() / end_schedule() pair anyway, the latter >> could notify any TXQs that became eligible during the scheduling round. > > Do we even need end_schedule()? It's hard to pass multiple things to a > single call (do you build a list?), so having > > start_schedule(), get_txq(), return_txq() > > would be sufficient? Well, start_schedule() / end_schedule() would be needed if we are going to add locking in mac80211? >> Also, instead of having the three different API functions >> (next_txq()/may_tx()/schedule_txq()), we could have get_txq(txq)/put_tx= q(txq) >> which would always need to be paired; but the argument to get_txq() >> could be optional, and if the driver passes NULL it means "give me the >> next available TXQ". > > I can't say I like this. It makes the meaning totally different: > > * with NULL: use the internal scheduler to determine which one is good > to use next > * non-NULL: essentially equivalent to may_tx() Yeah, it'll be two completely different uses for the same function; but there wouldn't be two different APIs to keep track of. I'm fine with keeping them as separately named functions. :) >> So for ath9k it would be: >>=20 >>=20 >> start_schedule(ac); >> while ((txq =3D get_txq(NULL)) { >> queue_aggregate(txq); >> put_txq(txq); >> } >> end_schedule(ac); >>=20 >> And for ath10k/iwlwifi it would be: >>=20 >> on_hw_notify(txq) { >> start_schedule(ac); >> if (txq =3D get_txq(txq)) { >> queue_packets(txq); >> put_txq(txq); >> } >> end_schedule(ac); >> } >>=20 >>=20 >> I think that would be simpler, API-wise? > > I can't say I see much point in overloading get_txq() that way. You'd > never use it the same way. > > Also, would you really start_schedule(ac) in the hw-managed case? If we decide mac80211 needs to do locking to prevent two threads from scheduling the same ac, that would also be needed for the hw-managed case? > It seems like not? Basically it seems to me that in the hw-managed > case all you need is may_tx()? And in fact, once you opt in you don't > even really need *that* since mac80211 can just return NULL from > get_skb()? Yeah, we could just throttle in get_skb(); the separate call was to avoid the overhead of the check for every packet. Typically, you'll pick a TXQ, then dequeue multiple packets from it in succession; with a separate call to may_tx(), you only do the check once, not for every packet... -Toke