From: Bruce Richardson <bruce.richardson@intel.com>
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Cc: Tyler Retzlaff <roretzla@linux.microsoft.com>,
Stephen Hemminger <stephen@networkplumber.org>,
"dev@dpdk.org" <dev@dpdk.org>, nd <nd@arm.com>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Subject: Re: [RFC] rte_ring: don't use always inline
Date: Fri, 6 May 2022 16:28:41 +0100 [thread overview]
Message-ID: <YnU+qQu+Rkqu+WM1@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <DBAPR08MB58148A2387457A31E13B5C1D98C59@DBAPR08MB5814.eurprd08.prod.outlook.com>
On Fri, May 06, 2022 at 03:12:32PM +0000, Honnappa Nagarahalli wrote:
> <snip>
> >
> > On Thu, May 05, 2022 at 10:59:32PM +0000, Honnappa Nagarahalli wrote:
> > > Thanks Stephen. Do you see any performance difference with this change?
> >
> > as a matter of due diligence i think a comparison should be made just to be
> > confident nothing is regressing.
> >
> > i support this change in principal since it is generally accepted best practice to
> > not force inlining since it can remove more valuable optimizations that the
> > compiler may make that the human can't see.
> > the optimizations may vary depending on compiler implementation.
> >
> > force inlining should be used as a targeted measure rather than blanket on
> > every function and when in use probably needs to be periodically reviewed and
> > potentially removed as the code / compiler evolves.
> >
> > also one other consideration is the impact of a particular compiler's force
> > inlining intrinsic/builtin is that it may permit inlining of functions when not
> > declared in a header. i.e. a function from one library may be able to be inlined
> > to another binary as a link time optimization. although everything here is in a
> > header so it's a bit moot.
> >
> > i'd like to see this change go in if possible.
> Like Stephen mentions below, I am sure we will have a for and against discussion here.
> As a DPDK community we have put performance front and center, I would prefer to go down that route first.
>
I ran some initial numbers with this patch, and the very quick summary of
what I've seen so far:
* Unit tests show no major differences, and while it depends on what
specific number you are interested in, most seem within margin of error.
* Within unit tests, the one number I mostly look at when considering
inlining is the "empty poll" cost, since I believe we should look to keep
that as close to zero as possible. In the past I've seen that number jump
from 3 cycles to 12 cycles due to missed inlining. In this case, it seem
fine.
* Ran a quick test with the eventdev_pipeline example app using SW eventdev,
as a test of an actual app which is fairly ring-heavy [used 8 workers
with 1000 cycles per packet hop]. (Thanks to Harry vH for this suggestion
of a workload)
* GCC 8 build - no difference observed
* GCC 11 build - approx 2% perf reduction observed
As I said, these are just some quick rough numbers, and I'll try and get
some more numbers on a couple of different platforms, see if the small
reduction seen is consistent or not. I may also test a few differnet
combinations/options in the eventdev test. It would be good if others also
tested on a few platforms available to them.
/Bruce
next prev parent reply other threads:[~2022-05-06 15:28 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-05 22:45 Stephen Hemminger
2022-05-05 22:59 ` Honnappa Nagarahalli
2022-05-05 23:10 ` Stephen Hemminger
2022-05-05 23:16 ` Stephen Hemminger
2022-05-06 1:37 ` Honnappa Nagarahalli
2022-05-06 7:24 ` Tyler Retzlaff
2022-05-06 15:12 ` Honnappa Nagarahalli
2022-05-06 15:28 ` Bruce Richardson [this message]
2022-05-06 16:33 ` Stephen Hemminger
2022-05-06 16:39 ` Bruce Richardson
2022-05-06 17:48 ` Konstantin Ananyev
2022-05-06 15:41 ` Stephen Hemminger
2022-05-06 16:38 ` Bruce Richardson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YnU+qQu+Rkqu+WM1@bricha3-MOBL.ger.corp.intel.com \
--to=bruce.richardson@intel.com \
--cc=Honnappa.Nagarahalli@arm.com \
--cc=dev@dpdk.org \
--cc=konstantin.ananyev@intel.com \
--cc=nd@arm.com \
--cc=roretzla@linux.microsoft.com \
--cc=stephen@networkplumber.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).