From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>
Subject: Re: [PATCH v4 2/2] ring: move the atomic load of head
	above the loop
Date: Fri, 2 Nov 2018 11:23:20 +0000
Message-ID: <VI1PR08MB3167C83B0158B32E31C03C838FCF0@VI1PR08MB3167.eurprd08.prod.outlook.com>
References: <1541066031-29125-1-git-send-email-gavin.hu@arm.com>
 <AM6PR08MB3672EB57F02379CD5649C6C998CF0@AM6PR08MB3672.eurprd08.prod.outlook.com>
 <VI1PR08MB3167D05E09C39C714E60904D8FCF0@VI1PR08MB3167.eurprd08.prod.outlook.com>
 <15443120.J8yKmjSJbt@xps>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Cc: Stephen Hemminger <stephen@networkplumber.org>, "dev@dpdk.org"
 <dev@dpdk.org>, "olivier.matz@6wind.com" <olivier.matz@6wind.com>,
 "chaozhu@linux.vnet.ibm.com" <chaozhu@linux.vnet.ibm.com>,
 "bruce.richardson@intel.com" <bruce.richardson@intel.com>,
 "konstantin.ananyev@intel.com" <konstantin.ananyev@intel.com>,
 "jerin.jacob@caviumnetworks.com" <jerin.jacob@caviumnetworks.com>,
 "stable@dpdk.org" <stable@dpdk.org>, nd <nd@arm.com>
To: Thomas Monjalon <thomas@monjalon.net>, Honnappa Nagarahalli
 <Honnappa.Nagarahalli@arm.com>
Return-path: <dev-bounces@dpdk.org>
In-Reply-To: <15443120.J8yKmjSJbt@xps>
Content-Language: en-US
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>



> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Friday, November 2, 2018 5:37 PM
> To: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Cc: Stephen Hemminger <stephen@networkplumber.org>; dev@dpdk.org;
> olivier.matz@6wind.com; chaozhu@linux.vnet.ibm.com;
> bruce.richardson@intel.com; konstantin.ananyev@intel.com;
> jerin.jacob@caviumnetworks.com; stable@dpdk.org; nd <nd@arm.com>
> Subject: Re: [PATCH v4 2/2] ring: move the atomic load of head above the
> loop
>=20
> 02/11/2018 08:15, Gavin Hu (Arm Technology China):
> >
> > > -----Original Message-----
> > > From: Honnappa Nagarahalli
> > > Sent: Friday, November 2, 2018 12:31 PM
> > > To: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Stephen
> > > Hemminger <stephen@networkplumber.org>
> > > Cc: dev@dpdk.org; thomas@monjalon.net; olivier.matz@6wind.com;
> > > chaozhu@linux.vnet.ibm.com; bruce.richardson@intel.com;
> > > konstantin.ananyev@intel.com; jerin.jacob@caviumnetworks.com;
> > > stable@dpdk.org; nd <nd@arm.com>
> > > Subject: RE: [PATCH v4 2/2] ring: move the atomic load of head above
> > > the loop
> > >
> > > <Fixing this to make the reply inline, making email plain text>
> > >
> > >
> > > On Thu, 1 Nov 2018 17:53:51 +0800
> > > Gavin Hu <mailto:gavin.hu@arm.com> wrote:
> > >
> > > > +* **Updated the ring library with C11 memory model.**
> > > > +
> > > > + Updated the ring library with C11 memory model including the
> > > > + following
> > > changes:
> > > > +
> > > > + * Synchronize the load and store of the tail
> > > > + * Move the atomic load of head above the loop
> > > > +
> > >
> > > Does this really need to be in the release notes? Is it a user
> > > visible change or just an internal/optimization and fix.
> > >
> > > [Gavin] There is no api changes, but this is a significant change as
> > > ring is fundamental and widely used, it decreases latency by 25% in
> > > our tests, it may do even better for cases with more contending
> > > producers/consumers or deeper depth of rings.
> > >
> > > [Honnappa] I agree with Stephen. Release notes should be written
> > > from DPDK user perspective. In the rte_ring case, the user has the
> > > option of choosing between c11 and non-c11 algorithms. Performance
> > > would be one of the criteria to choose between these 2 algorithms.
> > > IMO, it probably makes sense to indicate that the performance of c11
> > > based algorithm has been improved. However, I do not know what DPDK
> > > has followed historically regarding performance optimizations. I
> > > would prefer to follow whatever has been followed so far.
> > > I do not think that we need to document the details of the internal
> > > changes since it does not help the user make a decision.
> >
> > I read through the online guidelines for release notes, besides API and=
 new
> features, resolved issues which are significant and not newly introduced =
in
> this release cycle, should also be included.
> > In this case, the resolved issue existed for long time, across multiple
> release cycles and ring is a core lib, so it should be a candidate for re=
lease
> notes.
> >
> > https://doc.dpdk.org/guides-18.08/contributing/patches.html
> > section 5.5 says:
> > Important changes will require an addition to the release notes in
> doc/guides/rel_notes/.
> > See the Release Notes section of the Documentation Guidelines for detai=
ls.
> > https://doc.dpdk.org/guides-18.08/contributing/documentation.html#doc-
> > guidelines "Developers should include updates to the Release Notes
> > with patch sets that relate to any of the following sections:
> > New Features
> > Resolved Issues (see below)
> > Known Issues
> > API Changes
> > ABI Changes
> > Shared Library Versions
> > Resolved Issues should only include issues from previous releases that
> have been resolved in the current release. Issues that are introduced and
> then fixed within a release cycle do not have to be included here."
> >
> >      Suggested order in release notes items:
> >      * Core libs (EAL, mempool, ring, mbuf, buses)
> >      * Device abstraction libs and PMDs
>=20
> I agree with Honnappa.
> You don't need to give details, but can explain that performance of
> C11 version is improved.
>=20

V5 was submitted to indicate the improvement by the change, without giving =
more technical details, please have a review, thanks!