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From: "Gavin Hu (Arm Technology China)" <Gavin.Hu@arm.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>, Stephen Hemminger
<stephen@networkplumber.org>
CC: "dev@dpdk.org" <dev@dpdk.org>, "thomas@monjalon.net"
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Thread-Topic: [PATCH v4 2/2] ring: move the atomic load of head above the loop
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Date: Fri, 2 Nov 2018 07:15:48 +0000
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Subject: Re: [dpdk-dev] [PATCH v4 2/2] ring: move the atomic load of head
above the loop
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X-List-Received-Date: Fri, 02 Nov 2018 07:15:52 -0000
> -----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
>=20
> <Fixing this to make the reply inline, making email plain text>
>=20
>=20
> On Thu, 1 Nov 2018 17:53:51 +0800
> Gavin Hu <mailto:gavin.hu@arm.com> wrote:
>=20
> > +* **Updated the ring library with C11 memory model.**
> > +
> > + Updated the ring library with C11 memory model including the followin=
g
> changes:
> > +
> > + * Synchronize the load and store of the tail
> > + * Move the atomic load of head above the loop
> > +
>=20
> Does this really need to be in the release notes? Is it a user visible ch=
ange or
> just an internal/optimization and fix.
>=20
> [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.
>=20
> [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 ma=
kes
> 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 ha=
s
> been followed so far.
> I do not think that we need to document the details of the internal chang=
es
> 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 i=
n this release cycle, should also be included.
In this case, the resolved issue existed for long time, across multiple rel=
ease cycles and ring is a core lib, so it should be a candidate for release=
notes.=20
https://doc.dpdk.org/guides-18.08/contributing/patches.html
section 5.5 says:=20
Important changes will require an addition to the release notes in doc/guid=
es/rel_notes/.=20
See the Release Notes section of the Documentation Guidelines for details.
https://doc.dpdk.org/guides-18.08/contributing/documentation.html#doc-guide=
lines
"Developers should include updates to the Release Notes with patch sets tha=
t 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