Re: Linux SCTP performance question

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Hi David

I try to perform a performance test with a configuration consisting of a M3UA-ASP VM (client) served by 4 M3UA-SGP VMs (servers).
All the VMs are RHEL8.4.
The TCAP traffic is initiated by the ASP (10K DATA-Chunk/sec) and evenly distributed over the 4 SGPs which reflect the received traffic to the ASP.
Within a random interval (15 min to several hours) the ASP experiences an error when calling sctp_sendv() with ERRNO="Resource Temporarily Unavailable".
As I don't know what causes theese errors I am wondering if this is not a performance issue.

Referring to your performance test:
- Does 40K reflects/sec mean 40K Tx DATA-Chunk/sec and 40K Rx DATA-Chunk/sec ?
- Did you apply specific kernel parameters tuning (rmem, wmem, ...) ?
- Can you share the test program you were using ?

Thank you in advance for your help and support.


----- Mail original -----
De: "David Laight" <David.Laight@xxxxxxxxxx>
À: "o" <o.evistel@xxxxxxx>, "Marcelo Ricardo Leitner" <marcelo.leitner@xxxxxxxxx>
Cc: "linux-sctp" <linux-sctp@xxxxxxxxxxxxxxx>
Envoyé: Samedi 16 Juillet 2022 14:13:31
Objet: RE: Linux SCTP performance question

From: o.evistel@xxxxxxx
> Sent: 13 July 2022 13:59
> I am using linux-sctp as transport for SIGTRAN M3UA on RHEL 8.4 and I am
> using sctp_sendmsg() and sctp_recvmsg() to send/receive.
> I would like to know if the use of sctp_sendv() and sctp_recvv() enhances performances ?

Every copy to/from a user buffer has a small (but measurable) cost.
So anything with an iov[] array is a bit slower than an equivalent
call that only has a single buffer.
This is measurable when comparing sendmsg() and sendto() on (say)
a UDP socket.
OTOH it is all probably noise unless you are trying to send/receive
'silly numbers' of messages.

Reducing the number of system calls may help.
But the cost of recvmmsg() checking for a second message is
significantly greater than using epoll().
So unless you actually expect lots of messages it probably
isn't worth using.

Assuming you have disabled Nagle, then the biggest performance
gain will be from setting MSG_MORE when you know you have another
message to send.
Without that pretty much every M3UA message ends up in its own
ethernet packet.

You don't mention why you think you have a performance issue in SCTP.
I think we got 40000 reflects/sec from a tcap application over M3UA
and SCTP last time I measured out stack.


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