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Date: Thu, 12 Dec 2024 09:11:02 -0800
From: Stephen Hemminger <stephen@networkplumber.org>
To: Tudor Cornea <tudor.cornea@gmail.com>
Cc: linville@tuxdriver.com, ferruh.yigit@amd.com,
andrew.rybchenko@oktetlabs.ru, dev@dpdk.org
Subject: Re: [PATCH] net/af_packet: allow disabling packet fanout
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In-Reply-To: <20241212080442.1628366-1-tudor.cornea@gmail.com>
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On Thu, 12 Dec 2024 10:04:42 +0200
Tudor Cornea <tudor.cornea@gmail.com> wrote:
> This allows us to control whether the PMD will attempt to use
> the PACKET_FANOUT socket option, and allows the binary compiled
> against newer kernel headers to run on an older kernel, which
> lacks support for it.
>=20
> Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
Controlling fanout more is a good idea but not sure what this patch
is trying to do with it.
- DPDK minimum kernel version is now 4.19 so no point in worrying about
backward compatibility. According to man page for packet, fanout
was added in 3.1 kernel.
- It would be useful to allow application to control fanout in more detail.
According to man page:
=E2=80=A2 The load-balance mode PACKET_FANOUT_LB implements a=
round-
robin algorithm.
=E2=80=A2 PACKET_FANOUT_CPU selects the socket based on the CPU t=
hat the
packet arrived on.
=E2=80=A2 PACKET_FANOUT_ROLLOVER processes all data on a single =
socket,
moving to the next when one becomes backlogged.
=E2=80=A2 PACKET_FANOUT_RND selects the socket using a pseud=
o-random
number generator.
=E2=80=A2 PACKET_FANOUT_QM (available since Linux 3.14) sele=
cts the
socket using the recorded queue_mapping of the received skb.
The default should be for packet to behave like a hardware NIC if RSS is
enabled. And use a single queue if RSS is not enabled. The PMD kind of does
this now but not the same.