From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Aleksei Zakharov <zakharov.a.g@yandex.ru>
Cc: Network Development <netdev@vger.kernel.org>
Subject: Re: RPS arp processing
Date: Wed, 11 Dec 2019 13:59:38 -0500 [thread overview]
Message-ID: <CA+FuTSey4oa-WPRuAu8TAQFDO9e==e-+-SQ2p4237drq8GzOWQ@mail.gmail.com> (raw)
In-Reply-To: <83161576077966@vla4-87a00c2d2b1b.qloud-c.yandex.net>
On Wed, Dec 11, 2019 at 10:34 AM Aleksei Zakharov
<zakharov.a.g@yandex.ru> wrote:
>
> Hi, everyone
> Is it possible to balance ARP across CPUs with RPS?
> I don't clearly understand how hash is calulated for ARP packets, but it seems that it should consider source and target IPs.
The hash is derived by flow dissection:
get_rps_cpus
___skb_get_hash
skb_flow_dissect_flow_keys
This calls __skb_flow_dissector with the flow_keys_dissector
dissection program, which is initialized in
init_default_flow_dissectors from flow_keys_dissector_keys.
That program incorporates IPV4_ADDRS and IPV6_ADDRS. But that does not
apply to ARP packets. Contrast case ETH_P_IPV6 with case ETH_P_ARP in
__skb_flow_dissect.
The flow dissector calls __skb_flow_dissect_arp() for deeper
dissection, from which you could extract entropy for RPS. But the
flow_keys_dissector program does not have FLOW_DISSECTOR_KEY_ARP
enabled.
> In our current setup we have one l2 segment between external hardware routers and namespaces on linux server.
> When router sends ARP request, it is passed through server's physical port, then via openvswitch bridge it is copied to every namespace.
> We've found that all ARPs (for different destination ips and few source ips) are processed on one CPU inside namespaces. We use RPS, and most packets are balanced between all CPUs.
I suggest looking at the newer BPF flow dissector, which allows tuning
dissection to specific use cases, like yours.
> Kernel 4.15.0-65 from ubuntu 18.04.
>
> Might this issue be related to namespaces somehow?
>
> --
> Regards,
> Aleksei Zakharov
>
next prev parent reply other threads:[~2019-12-11 19:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-11 15:26 RPS arp processing Aleksei Zakharov
2019-12-11 18:59 ` Willem de Bruijn [this message]
2019-12-11 22:08 ` Aleksei Zakharov
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='CA+FuTSey4oa-WPRuAu8TAQFDO9e==e-+-SQ2p4237drq8GzOWQ@mail.gmail.com' \
--to=willemdebruijn.kernel@gmail.com \
--cc=netdev@vger.kernel.org \
--cc=zakharov.a.g@yandex.ru \
/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).