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From: Thomas Monjalon <thomas@monjalon.net>
To: Bing Zhao <bingz@nvidia.com>,
 Stephen Hemminger <stephen@networkplumber.org>
Cc: Slava Ovsiienko <viacheslavo@nvidia.com>, Matan Azrad <matan@nvidia.com>, 
 dev <dev@dpdk.org>, Dariusz Sosnowski <dsosnowski@nvidia.com>,
 Suanming Mou <suanmingm@nvidia.com>, Raslan Darawsheh <rasland@nvidia.com>
Subject: Re: [PATCH v2 2/3] net/mlx5: add new devarg for Tx queue consecutive
 memory
Date: Thu, 26 Jun 2025 17:21:55 +0200
Message-ID: <5112176.f0I1acK8xe@thomas>
In-Reply-To: <20250626072954.6ca04456@hermes.local>
References: <20250623183456.130666-1-bingz@nvidia.com>
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26/06/2025 16:29, Stephen Hemminger:
> On Thu, 26 Jun 2025 13:18:18 +0000
> Bing Zhao <bingz@nvidia.com> wrote:
>=20
> > Hi Stephen,
> >=20
> > Thanks for your review and comments. I will add the description about t=
he new devarg in our mlx5.rst file to have a detailed description.
> > Indeed, after some review and internal call discussion with our datapat=
h experts. We would like to change the devarg a little bit but not only 0 /=
 1 as a chicken bit.
> >=20
> > Since the memory accessing footprints and orders may impact the perform=
ance. In the perf test, we found that the alignment of the queue address ma=
y impact it. The basic starting address alignment is system page size, but =
it can be bigger.
> > So the new devarg use will be the log value of the alignment for all qu=
eues=E2=80=99 starting addresses. And on different CPU architectures / gene=
rations that have different LLC systems can try to use different alignment =
to get the best performance without rebuilding the binary application from =
the source code and it is configurable. WDYT?
>=20
> Please make it automatic, the driver already has too many config bits.
> The users should just get good performance with the default.
> If driver needs to it should look at any/all system info to determine wha=
t the best setting is.

The default would be good enough, but it looks very difficult to know the b=
est value.
That's why the idea is to allow some tuning here.

I agree there are too many devargs for most users,
but at the same time DPDK is a project to get the best performance,
that's why there are so many tuning possible.
I think we can meet both goals by making clear which options are for advanc=
ed tuning,
so a basic user will not mess with with such options which have a good defa=
ult by the way.