Re: Full 40Gbps with i40e for large packets?

[Willy Tarreau <w@1wt.eu>]

On Fri, Jun 24, 2022 at 09:23:51PM +0530, Srivats P wrote:
> Yes, I'm using 40G copper. 1518 byte is including FCS and no VLANs, so
> the pps expected to fully fill the pipe as you calculate rightly is
> 3250975 or 3.25 Mpps.

OK.

> The rate I get varies continuously between 3.19 and 3.22 Mpps and very
> rarely goes up to 3.24 Mpps. The few times I've seen 3.24 Mpps is at
> the immediate start of a run, but not afterwards - a behaviour I'm not
> able to explain.
> 
> I'm trying to understand why I get a lower rate than 3.250975 Mpps and
> what I need to do to get the full pps rate.

In other contexts I've faced causes such as too large tx_irq delay,
causing the tx ring to be empty when the code was able to deliver
more, and too small PCIe payload sizes (I remember having had to
change it to 4096 in a machine's BIOS years ago for a 100G test).

Beyond this I have no idea :-)

Willy