Return-path: Received: from mail-pa0-f45.google.com ([209.85.220.45]:42420 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751973AbbBJMzB (ORCPT ); Tue, 10 Feb 2015 07:55:01 -0500 Message-ID: <1423572896.28434.13.camel@edumazet-glaptop2.roam.corp.google.com> (sfid-20150210_135510_394373_791B8B50) Subject: Re: Throughput regression with `tcp: refine TSO autosizing` From: Eric Dumazet To: Michal Kazior Cc: Neal Cardwell , linux-wireless , Network Development , Eyal Perry Date: Tue, 10 Feb 2015 04:54:56 -0800 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> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-wireless-owner@vger.kernel.org List-ID: 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; > + } > + Hi Michal This is almost it ;) As I said you must do this using u64 arithmetics, we still support 32bit kernels. Also, >> 20 instead of / 1000000 introduces a 5% error, I would use a plain divide, as the compiler will use a reciprocal divide (ie : a multiply) We use >> 10 instead of /1000 because a 2.4 % error is probably okay. ewma_add(&ar->tx_delay_us, ktime_to_ns(ktime_sub(ktime_get(), skb_cb->stamp)) / NSEC_PER_USEC); u64 val = (u64)ewma_read(&ar->tx_delay_us) * msdu->sk->sk_pacing_rate; do_div(val, USEC_PER_SEC); ACCESS_ONCE(msdu->sk->sk_tx_completion_delay_cushion) = (u32)val; (WRITE_ONCE() would be better for new kernels, but ACCESS_ONCE() is ok since we probably want to backport to stable kernels) Thanks