public inbox for netdev@vger.kernel.org 
 help / color / mirror / Atom feed

From: ValdikSS <iam@valdikss•org.ru>
To: Guus Sliepen <guus@tinc-vpn•org>
Cc: Stephen Hemminger <stephen@networkplumber•org>,
	Willem de Bruijn <willemdebruijn.kernel@gmail•com>,
	David Miller <davem@davemloft•net>,
	Tom Herbert <tom@herbertland•com>,
	netdev@vger•kernel.org
Subject: Re: Best way to reduce system call overhead for tun device I/O?
Date: Mon, 4 Apr 2016 16:35:13 +0300	[thread overview]
Message-ID: <57026D91.4090207@valdikss.org.ru> (raw)

I'm trying to increase OpenVPN throughput by optimizing tun manipulations, too.
Right now I have more questions than answers.

I get about 800 Mbit/s speeds via OpenVPN with authentication and encryption disabled on a local machine with OpenVPN server and client running in a different
network namespaces, which use veth for networking, with 1500 MTU on a TUN interface. This is rather limiting. Low-end devices like SOHO routers could only
achieve 15-20 Mbit/s via OpenVPN with encryption with a 560 MHz CPU.
Increasing MTU reduces overhead. You can get > 5GBit/s if you set 16000 MTU on a TUN interface.
That's not only OpenVPN related. All the tunneling software I tried can't achieve gigabit speeds without encryption on my machine with MTU 1500. Didn't test
tinc though.

TUN supports various offloading techniques: GSO, TSO, UFO, just as hardware NICs. From what I understand, if we use GSO/GRO for TUN, we would be able to receive
send small packets combined in a huge one with one send/recv call with MTU 1500 on a TUN interface, and the performance should increase and be just as it now
with increased MTU. But there is a very little information of how to use offloading with TUN.
I've found an old example code which creates TUN interface with GSO support (TUN_VNET_HDR), does NAT and echoes TUN data to stdout, and a script to run two
instances of this software connected with a pipe. But it doesn't work for me, I never see any combined frames (gso_type is always 0 in a virtio_net_hdr header).
Probably I did something wrong, but I'm not sure what exactly is wrong.

Here's said application: http://ovrload.ru/f/68996_tun.tar.gz

The questions are as follows:

 1. Do I understand correctly that GSO/GRO would have the same effect as increasing MTU on TUN interface?
 2. How GRO/GSO is different from TSO, UFO?
 3. Can we get and send combined frames directly from/to NIC with offloading support?
 4. How to implement GRO/GSO, TSO, UFO? What should be the logic behind it?


Any reply is greatly appreciated.

P.S. this could be helpful: https://ldpreload.com/p/tuntap-notes.txt

> I'm trying to reduce system call overhead when reading/writing to/from a
> tun device in userspace. For sockets, one can use sendmmsg()/recvmmsg(),
> but a tun fd is not a socket fd, so this doesn't work. I'm see several
> options to allow userspace to read/write multiple packets with one
> syscall:
>
> - Implement a TX/RX ring buffer that is mmap()ed, like with AF_PACKET
>   sockets.
>
> - Implement a ioctl() to emulate sendmmsg()/recvmmsg().
>
> - Add a flag that can be set using TUNSETIFF that makes regular
>   read()/write() calls handle multiple packets in one go.
>
> - Expose a socket fd to userspace, so regular sendmmsg()/recvmmsg() can
>   be used. There is tun_get_socket() which is used internally in the
>   kernel, but this is not exposed to userspace, and doesn't look trivial
>   to do either.
>
> What would be the right way to do this?
>
> -- 
> Met vriendelijke groet / with kind regards,
>      Guus Sliepen <guus@tinc-vpn•org>

next             reply	other threads:[~2016-04-04 13:35 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-04-04 13:35 ValdikSS [this message]
2016-04-04 17:28 ` Best way to reduce system call overhead for tun device I/O? Stephen Hemminger
     [not found] <57026C8F.8050406@valdikss.org.ru>
2016-04-04 14:31 ` Guus Sliepen
  -- strict thread matches above, loose matches on Subject: below --
2016-03-29 22:40 Guus Sliepen
2016-03-31 21:18 ` Tom Herbert
2016-03-31 21:20   ` David Miller
2016-03-31 22:28     ` Guus Sliepen
2016-03-31 23:39       ` Stephen Hemminger
2016-04-03 23:03         ` Willem de Bruijn
2016-04-04 14:40           ` Guus Sliepen

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=57026D91.4090207@valdikss.org.ru \
    --to=iam@valdikss$(echo .)org.ru \
    --cc=davem@davemloft$(echo .)net \
    --cc=guus@tinc-vpn$(echo .)org \
    --cc=netdev@vger$(echo .)kernel.org \
    --cc=stephen@networkplumber$(echo .)org \
    --cc=tom@herbertland$(echo .)com \
    --cc=willemdebruijn.kernel@gmail$(echo .)com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox