Re: [dpdk-dev] [PATCH] net/af_xdp: optimisations to improve packet loss

["Loftus, Ciara" <ciara.loftus@intel.com>]

> 
> On Fri, 12 Jun 2020 14:17:46 +0000
> Ciara Loftus <ciara.loftus@intel.com> wrote:
> 
> > This commit makes some changes to the AF_XDP PMD in an effort to
> improve
> > its packet loss characteristics.
> >
> > 1. In the case of failed transmission due to inability to reserve a tx
> > descriptor, the PMD now pulls from the completion ring, issues a syscall
> > in which the kernel attempts to complete outstanding tx operations, then
> > tries to reserve the tx descriptor again. Prior to this we dropped the
> > packet after the syscall and didn't try to re-reserve.
> >
> > 2. During completion ring cleanup, always pull as many entries as possible
> > from the ring as opposed to the batch size or just how many packets
> > we're going to attempt to send. Keeping the completion ring emptier
> should
> > reduce failed transmissions in the kernel, as the kernel requires space in
> > the completion ring to successfully tx.
> >
> > 3. Size the fill ring as twice the receive ring size which may help reduce
> > allocation failures in the driver.
> >
> > With these changes, a benchmark which measured the packet rate at
> which
> > 0.01% packet loss could be reached improved from ~0.1G to ~3Gbps.
> >
> > Signed-off-by: Ciara Loftus <ciara.loftus@intel.com>
> 
> You might want to add the ability to emulate a tx_free threshold
> by pulling more completions earlier.

Thanks for the suggestion. I've implemented it in the v2.

Ciara