Re: xdpsock poll syscall CPU 100%

[Magnus Karlsson <magnus.karlsson@gmail.com>]

On Fri, Feb 21, 2020 at 9:30 AM Eelco Chaudron <echaudro@redhat.com> wrote:
>
>
>
> On 20 Feb 2020, at 23:49, William Tu wrote:
>
> > Hi,
> >
> > I'm trying to save some CPU cycles when there is no packet arrives.
> > I enable the poll syscall option of xdpsock, by doing
> >
> > $ ./xdpsock -r -p -S -i ens16
> >  sock0@ens160:0 rxdrop xdp-skb poll()
> >                 pps         pkts        1.00
> > rx              0           0
> > tx              0           0
> >
> > Since there is no packet coming, I though by calling poll()
> > system call, the xdpsock process will be blocked and CPU utilization
> > should be way under 100%. However, I'm still seeing 100%
> > CPU utilization. Am I understanding this correctly?
>
> Hi William, I can remember I saw this in the past two with this code. It
> had something to do with the way xdpsock waits for the buffers to be
> free’ ed by the kernel. What I can remember it had something to do
> with the veth interfaces also.
>
> I do remember that I fixed it in the tutorial for AF_XDP:
> https://github.com/xdp-project/xdp-tutorial/blob/master/advanced03-AF_XDP/af_xdp_user.c

Eelco,

Do you remember exactly what you had to fix in the xdpsock sample?
Your tutorial is quite a rewrite so it is hard for me to tell exactly
which of all the changes that fix this problem. The reason I ask is
that it would be nice to fix this in the sample too.

Thanks: Magnus

> Maybe you can see if you have the same problem with this example.
>
> //Eelco
>
>
> > Thanks,
> > William
>