From: "Laatz, Kevin" <kevin.laatz@intel.com>
To: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Jonathan Lemon <jonathan.lemon@gmail.com>,
netdev@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
bjorn.topel@intel.com, magnus.karlsson@intel.com,
bpf@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
bruce.richardson@intel.com, ciara.loftus@intel.com
Subject: Re: [PATCH 00/11] XDP unaligned chunk placement support
Date: Fri, 28 Jun 2019 17:19:09 +0100 [thread overview]
Message-ID: <f0ca817a-02b4-df22-d01b-7bc07171a4dc@intel.com> (raw)
In-Reply-To: <20190627142534.4f4b8995@cakuba.netronome.com>
On 27/06/2019 22:25, Jakub Kicinski wrote:
> On Thu, 27 Jun 2019 12:14:50 +0100, Laatz, Kevin wrote:
>> On the application side (xdpsock), we don't have to worry about the user
>> defined headroom, since it is 0, so we only need to account for the
>> XDP_PACKET_HEADROOM when computing the original address (in the default
>> scenario).
> That assumes specific layout for the data inside the buffer. Some NICs
> will prepend information like timestamp to the packet, meaning the
> packet would start at offset XDP_PACKET_HEADROOM + metadata len..
Yes, if NICs prepend extra data to the packet that would be a problem for
using this feature in isolation. However, if we also add in support for
in-order
RX and TX rings, that would no longer be an issue. However, even for NICs
which do prepend data, this patchset should not break anything that is
currently
working.
>
> I think that's very limiting. What is the challenge in providing
> aligned addresses, exactly?
The challenges are two-fold:
1) it prevents using arbitrary buffer sizes, which will be an issue
supporting e.g. jumbo frames in future.
2) higher level user-space frameworks which may want to use AF_XDP, such
as DPDK, do not currently support having buffers with 'fixed' alignment.
The reason that DPDK uses arbitrary placement is that:
- it would stop things working on certain NICs which need the
actual writable space specified in units of 1k - therefore we need 2k +
metadata space.
- we place padding between buffers to avoid constantly hitting
the same memory channels when accessing memory.
- it allows the application to choose the actual buffer size it
wants to use.
We make use of the above to allow us to speed up processing
significantly and also reduce the packet buffer memory size.
Not having arbitrary buffer alignment also means an AF_XDP driver
for DPDK cannot be a drop-in replacement for existing drivers in those
frameworks. Even with a new capability to allow an arbitrary buffer
alignment, existing apps will need to be modified to use that new
capability.
next parent reply other threads:[~2019-06-28 16:19 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190620083924.1996-1-kevin.laatz@intel.com>
[not found] ` <FA8389B9-F89C-4BFF-95EE-56F702BBCC6D@gmail.com>
[not found] ` <ef7e9469-e7be-647b-8bb1-da29bc01fa2e@intel.com>
[not found] ` <20190627142534.4f4b8995@cakuba.netronome.com>
2019-06-28 16:19 ` Laatz, Kevin [this message]
2019-06-28 16:51 ` [PATCH 00/11] XDP unaligned chunk placement support Björn Töpel
2019-06-28 20:08 ` Jakub Kicinski
2019-06-28 20:25 ` Jakub Kicinski
2019-06-28 20:29 ` Jonathan Lemon
2019-07-01 14:58 ` Laatz, Kevin
[not found] ` <07e404eb-f712-b15a-4884-315aff3f7c7d@intel.com>
2019-07-01 21:20 ` Jakub Kicinski
2019-07-02 9:27 ` Richardson, Bruce
2019-07-02 16:33 ` Jonathan Lemon
2019-06-20 9:09 Kevin Laatz
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=f0ca817a-02b4-df22-d01b-7bc07171a4dc@intel.com \
--to=kevin.laatz@intel.com \
--cc=ast@kernel.org \
--cc=bjorn.topel@intel.com \
--cc=bpf@vger.kernel.org \
--cc=bruce.richardson@intel.com \
--cc=ciara.loftus@intel.com \
--cc=daniel@iogearbox.net \
--cc=intel-wired-lan@lists.osuosl.org \
--cc=jakub.kicinski@netronome.com \
--cc=jonathan.lemon@gmail.com \
--cc=magnus.karlsson@intel.com \
--cc=netdev@vger.kernel.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).