From mboxrd@z Thu Jan 1 00:00:00 1970
Return-Path: <dev-bounces@dpdk.org>
Received: from dpdk.org (dpdk.org [92.243.14.124])
by inbox.dpdk.org (Postfix) with ESMTP id D7E01A00C5;
Sun, 5 Jul 2020 22:41:55 +0200 (CEST)
Received: from [92.243.14.124] (localhost [127.0.0.1])
by dpdk.org (Postfix) with ESMTP id 598531DA45;
Sun, 5 Jul 2020 22:41:55 +0200 (CEST)
Received: from out5-smtp.messagingengine.com (out5-smtp.messagingengine.com
[66.111.4.29]) by dpdk.org (Postfix) with ESMTP id 37B6E1DA27
for <dev@dpdk.org>; Sun, 5 Jul 2020 22:41:53 +0200 (CEST)
Received: from compute7.internal (compute7.nyi.internal [10.202.2.47])
by mailout.nyi.internal (Postfix) with ESMTP id C49EB5C009D;
Sun, 5 Jul 2020 16:41:52 -0400 (EDT)
Received: from mailfrontend2 ([10.202.2.163])
by compute7.internal (MEProxy); Sun, 05 Jul 2020 16:41:52 -0400
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=monjalon.net; h=
from:to:cc:subject:date:message-id:in-reply-to:references
:mime-version:content-transfer-encoding:content-type; s=fm1; bh=
U4Y/XcdunMnRxCMFQRBoKeYUTurD9HA3idElu7SLOg8=; b=Kb39VEsxUAHRRuW1
YWVl5ZVnGLhyRLtaYs2R9nzfSVoHphKv3HkRFPK4/5uDZFx11UQmixDhhquy+b8k
kJxmilbX69hqyAiaCIN5qOeLpbK1e1adP9ChHKEkuEMF+HFcn1O+aa7yRatlIawC
WfP/X/G63BwItaPzOa+iHhhea5IvL8K9AFrEPoQJajpgdBQvQcLNAcQfwZ4EyxWf
HiOKVrZEjsD06M16mXw3zKuiMrQ7JIeK+E8d/HhQGl9K1Vt1V7R7G0f1ruAmFoYj
98SvDXD8rnAXE2B/ijxCU/zzEZjC+Rt9NrlhBOS+FDZCvZf/SdBGOHK52OVI6dPo
2NDteA==
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=
messagingengine.com; h=cc:content-transfer-encoding:content-type
:date:from:in-reply-to:message-id:mime-version:references
:subject:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender
:x-sasl-enc; s=fm3; bh=U4Y/XcdunMnRxCMFQRBoKeYUTurD9HA3idElu7SLO
g8=; b=TT0oG6b81T1qZH8MzfIarih6TT7dt4nfht5x7OV6g1VWzq4wihC/FUA6k
hCkf+f8RxPlwEkYNy+982PzNGEP4jfhu7jT/F04pEhhj0bB6Qw498FYUw1TcZ0ns
TzxLO7EJ4oILKH6hb5oP1G7zqNH4/gvSsfZ1w+KhXWmpGrIzqHt6ysnqIQVfb0eQ
Vh1v5XEStJfqIm4uN4N09bVlYtdDizpZkVE+YUHvPUTF2DvBHjzoRjgXHMpOo4D3
cgdSMlWDDFcqWQo99zTSVa1aO3VoRoJdFsnGbofzZlZLRbdawK8Fh1xxHTauvHix
yS4rO3UPwXVeiyLT5aymvTa9EOlJA==
X-ME-Sender: <xms:EDsCX1C-EyUJeMDFR7DlTeUWdESaL2-xPV9xXxgzgrrysffiXh1d-A>
X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduiedruddugdduheehucetufdoteggodetrfdotf
fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen
uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne
cujfgurhephffvufffkfgjfhgggfgtsehtufertddttddvnecuhfhrohhmpefvhhhomhgr
shcuofhonhhjrghlohhnuceothhhohhmrghssehmohhnjhgrlhhonhdrnhgvtheqnecugg
ftrfgrthhtvghrnhepudeggfdvfeduffdtfeeglefghfeukefgfffhueejtdetuedtjeeu
ieeivdffgeehnecukfhppeejjedrudefgedrvddtfedrudekgeenucevlhhushhtvghruf
hiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpehthhhomhgrshesmhhonhhjrghl
ohhnrdhnvght
X-ME-Proxy: <xmx:EDsCXzgEGqDR-1z5dmH31Fqqd2XhkMv2woyQiqYCuS7KJljftcR49Q>
<xmx:EDsCXwl03vWGOg4YdIA0vV_lSOlqIQYCVuGT4cJ3hMaWFsUgRzk_dA>
<xmx:EDsCX_zpJpfdUX--ukGGYbXipEt4d4m9UmfV1WQ66w3GsAYU7x1cZQ>
<xmx:EDsCX9K4GhjPSTelNbLE0199xK4ZGar7KpQfP-Un9JwFPBrKImXHDw>
Received: from xps.localnet (184.203.134.77.rev.sfr.net [77.134.203.184])
by mail.messagingengine.com (Postfix) with ESMTPA id C1F08306AAA6;
Sun, 5 Jul 2020 16:41:51 -0400 (EDT)
From: Thomas Monjalon <thomas@monjalon.net>
To: cristian.dumitrescu@intel.com, jasvinder.singh@intel.com
Cc: dev@dpdk.org, Alan Dewar <alan.dewar@att.com>, alangordondewar@gmail.com
Date: Sun, 05 Jul 2020 22:41:50 +0200
Message-ID: <1765563.QPqcEuCtyy@thomas>
In-Reply-To: <20200625095930.18429-1-alan.dewar@att.com>
References: <20200416084821.12591-1-alan.dewar@att.com>
<20200625095930.18429-1-alan.dewar@att.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Subject: Re: [dpdk-dev] [PATCH v2] sched: fix port time rounding error
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: DPDK patches and discussions <dev.dpdk.org>
List-Unsubscribe: <https://mails.dpdk.org/options/dev>,
<mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://mails.dpdk.org/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <https://mails.dpdk.org/listinfo/dev>,
<mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>
Cristian, Jasvinder, please review.
25/06/2020 11:59, alangordondewar@gmail.com:
> From: Alan Dewar <alan.dewar@att.com>
>
> The QoS scheduler works off port time that is computed from the number
> of CPU cycles that have elapsed since the last time the port was
> polled. It divides the number of elapsed cycles to calculate how
> many bytes can be sent, however this division can generate rounding
> errors, where some fraction of a byte sent may be lost.
>
> Lose enough of these fractional bytes and the QoS scheduler
> underperforms. The problem is worse with low bandwidths.
>
> To compensate for this rounding error this fix doesn't advance the
> port's time_cpu_cycles by the number of cycles that have elapsed,
> but by multiplying the computed number of bytes that can be sent
> (which has been rounded down) by number of cycles per byte.
> This will mean that port's time_cpu_cycles will lag behind the CPU
> cycles momentarily. At the next poll, the lag will be taken into
> account.
>
> v2:
> If the cycles value wraps (100 year+) reset the port's cpu cycle back
> to zero.
>
> Fixes: de3cfa2c98 ("sched: initial import")
>
> Signed-off-by: Alan Dewar <alan.dewar@att.com>
> ---
> lib/librte_sched/rte_sched.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/lib/librte_sched/rte_sched.c b/lib/librte_sched/rte_sched.c
> index c0983ddda..7c022cd61 100644
> --- a/lib/librte_sched/rte_sched.c
> +++ b/lib/librte_sched/rte_sched.c
> @@ -222,6 +222,7 @@ struct rte_sched_port {
> uint64_t time_cpu_bytes; /* Current CPU time measured in bytes */
> uint64_t time; /* Current NIC TX time measured in bytes */
> struct rte_reciprocal inv_cycles_per_byte; /* CPU cycles per byte */
> + uint64_t cycles_per_byte;
>
> /* Grinders */
> struct rte_mbuf **pkts_out;
> @@ -852,6 +853,7 @@ rte_sched_port_config(struct rte_sched_port_params *params)
> cycles_per_byte = (rte_get_tsc_hz() << RTE_SCHED_TIME_SHIFT)
> / params->rate;
> port->inv_cycles_per_byte = rte_reciprocal_value(cycles_per_byte);
> + port->cycles_per_byte = cycles_per_byte;
>
> /* Grinders */
> port->pkts_out = NULL;
> @@ -2673,16 +2675,21 @@ static inline void
> rte_sched_port_time_resync(struct rte_sched_port *port)
> {
> uint64_t cycles = rte_get_tsc_cycles();
> - uint64_t cycles_diff = cycles - port->time_cpu_cycles;
> + uint64_t cycles_diff;
> uint64_t bytes_diff;
> uint32_t i;
>
> + if (cycles < port->time_cpu_cycles)
> + port->time_cpu_cycles = 0;
> +
> + cycles_diff = cycles - port->time_cpu_cycles;
> /* Compute elapsed time in bytes */
> bytes_diff = rte_reciprocal_divide(cycles_diff << RTE_SCHED_TIME_SHIFT,
> port->inv_cycles_per_byte);
>
> /* Advance port time */
> - port->time_cpu_cycles = cycles;
> + port->time_cpu_cycles +=
> + (bytes_diff * port->cycles_per_byte) >> RTE_SCHED_TIME_SHIFT;
> port->time_cpu_bytes += bytes_diff;
> if (port->time < port->time_cpu_bytes)
> port->time = port->time_cpu_bytes;
>