Re: Expected SCTP DATA chunk per second performance

[Harald Welte <laforge@gnumonks.org>]

Hi Michael,

On Mon, Mar 02, 2020 at 02:28:26PM +0100, Michael Tuexen wrote:

> I consider it a bug. 

Agreed.

> Nagle normally is implemented by not sending small packets.
> From the numbers you provided, I guess the SCTP packets are about 1500 bytes. But
> I guess Linux has an MTU on the loopback interface which is much larger.

Actually, it depends on the type of sender code I use.  With Eclipse TITAN IPL4asp
(my ultimate target for writing the tests), the packets indeed are pnly 1500 bytes
in size.

When using the small C program attached, I'm seeing ~34 kByte sized IP
packets on loopback, but only at 500-510 DATA chunks per second overall
rate.

When disabling NAGLE ('client -d' of the attached program), I'm getting
much higher throughput, but there is no single IP packet with more than
a single DATA chunk inside at all anymore.  The latter is expected on
the one hand side (every syscall goes all the way to build a packet and
send it), but given at the high sender rate I would have expected that
every so often multiple DATA chunks arrive from userspace before a
packet has been sent (socket send buffer)?  In any case, no complaints
in this case.

Also interesting: With the application code (TITAN) in place, I am
seeing higher DATA chunk throughput over actual Ethernet than I'm seeing
over loopback.

I'd appreciate any feedback from the lksctp hackers here if I should
open a bugzilla issue about the poor performance with Nagle.

Regards,
	Harald

-- 
- Harald Welte <laforge@gnumonks.org>           http://laforge.gnumonks.org/
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