Return-path: Received: from mail-wg0-f42.google.com ([74.125.82.42]:65312 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751252AbbBLHsZ convert rfc822-to-8bit (ORCPT ); Thu, 12 Feb 2015 02:48:25 -0500 Received: by mail-wg0-f42.google.com with SMTP id x13so8304812wgg.1 for ; Wed, 11 Feb 2015 23:48:24 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <1422537297.21689.15.camel@edumazet-glaptop2.roam.corp.google.com> <1422628835.21689.95.camel@edumazet-glaptop2.roam.corp.google.com> <1422903136.21689.114.camel@edumazet-glaptop2.roam.corp.google.com> <1422926330.21689.138.camel@edumazet-glaptop2.roam.corp.google.com> <1422973660.907.10.camel@edumazet-glaptop2.roam.corp.google.com> <1423051045.907.108.camel@edumazet-glaptop2.roam.corp.google.com> <1423053531.907.115.camel@edumazet-glaptop2.roam.corp.google.com> <1423055810.907.125.camel@edumazet-glaptop2.roam.corp.google.com> <1423056591.907.130.camel@edumazet-glaptop2.roam.corp.google.com> <1423084303.31870.15.camel@edumazet-glaptop2.roam.corp.google.com> <1423141038.31870.38.camel@edumazet-glaptop2.roam.corp.google.com> <1423142342.31870.49.camel@edumazet-glaptop2.roam.corp.google.com> <1423147286.31870.59.camel@edumazet-glaptop2.roam.corp.google.com> <1423156205.31870.86.camel@edumazet-glaptop2.roam.corp.google.com> <1423230001.31870.128.camel@edumazet-glaptop2.roam.corp.google.com> <1423230785.31870.131.camel@edumazet-glaptop2.roam.corp.google.com> <1423494690.31870.189.camel@edumazet-glaptop2.roam.corp.google.com> <1423577962.2215.2.camel@sipsolutions.net> Date: Thu, 12 Feb 2015 08:48:24 +0100 Message-ID: (sfid-20150212_084834_128537_BDF7E327) Subject: Re: Throughput regression with `tcp: refine TSO autosizing` From: Michal Kazior To: Johannes Berg Cc: Eric Dumazet , Neal Cardwell , linux-wireless , Network Development , Eyal Perry Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 11 February 2015 at 09:57, Michal Kazior wrote: > On 10 February 2015 at 15:19, Johannes Berg wrote: >> On Tue, 2015-02-10 at 11:33 +0100, Michal Kazior wrote: >> >>> + if (msdu->sk) { >>> + ewma_add(&ar->tx_delay_us, >>> + ktime_to_ns(ktime_sub(ktime_get(), skb_cb->stamp)) / >>> + NSEC_PER_USEC); >>> + >>> + ACCESS_ONCE(msdu->sk->sk_tx_completion_delay_cushion) = >>> + (ewma_read(&ar->tx_delay_us) * >>> + msdu->sk->sk_pacing_rate) >> 20; >>> + } >> >> To some extent, every wifi driver is going to have this problem. Perhaps >> we should do this in mac80211? > > Good point. I was actually thinking about it. I can try cooking a > patch unless you want to do it yourself :-) I've taken a look into this. The most obvious place to add the timestamp for each packet would be ieee80211_tx_info (i.e. the skb->cb[48]). The problem is it's very tight there. Even squeezing 2 bytes (allowing up to 64ms of tx completion delay which I'm worried won't be enough) will be troublesome. Some drivers already use every last byte of their allowance on 64bit archs (e.g. ar5523 uses entire 40 bytes of driver_data). I wonder if it's okay to bump skb->cb to 56 bytes to avoid the cascade of changes required to implement the tx completion delay accounting? Michał