[PATCH] net/mlx5: fix FD configuration for Rx interrupt

[Michael Baum]

On Thu, Mar 10, 2022 at 6:16 PM Thomas Monjalon <thomas at monjalon.net> wrote: 
> 
> 10/03/2022 16:12, David Marchand:
> > On Thu, Mar 10, 2022 at 2:19 PM Michael Baum <michaelba at nvidia.com>
> wrote:
> > >
> > > The mlx5_rx_intr_vec_enable() function allocates queue vector and
> > > fill FD list for Rx interrupts.
> > >
> > > The driver wrongly configured the FD with a non-blocking flag which
> > > prevent waiting on this FD.
> > >
> > > This patch removes O_NONBLOCK flag adding.
> >
> > - Maybe I deserve a Reported-by: credit on this issue.

Hi David,

You are right, you should have get the credit.

> > I sent a proposal to make use of Rx interrupts in OVS
> >
> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> hwork.ozlabs.org%2Fproject%2Fopenvswitch%2Fpatch%2F20220304161132.2
> 2065-1-
> david.marchand%40redhat.com%2F&data=04%7C01%7Cmichaelba%40n
> vidia.com%7C3679e1e70986425d465b08da02b14b34%7C43083d15727340c1b7
> db39efd9ccc17a%7C0%7C0%7C637825257758477604%7CUnknown%7CTWFpb
> GZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI
> 6Mn0%3D%7C3000&sdata=LamFMZTLgZzQoUDBYAGn2aL9z7RWylWCkn
> q2SGFuKOY%3D&reserved=0.
> > And that's when I noticed that mlx5 rx fds were waking OVS too often
> > and reported it to mlx5 maintainers.
> >
> >
> > - Testing this patch by starting dpdk-l3fwd-power example (and no
> > traffic sent at all):
> >
> > # strace -r -f ./dpdk-dir/v21.11/examples/dpdk-l3fwd-power --lcores
> > 0 at 3,1 at 5 -a 0000:82:00.0 --in-memory -- -p 0x1 -P --config '(0,0,1)'
> > ...
> > [pid 534983]      0.000348 epoll_wait(26, [], 1, 10) = 0
> > [pid 534983]      0.010082 read(24,
> >
> > For some reason, there is an event available for fd 18 right away
> > (which is the issue in the first place).

I don't understand who is FD 18, I cannot see it in your log

> > When reading this fd, read() blocks until an actual packet is received.
> >
> > Then, I send exactly one packet:
> > [pid 534983]      0.010082 read(24, "@\217:\370\21\0\0\0", 136) = 8
> > [pid 534983]      9.228478 epoll_wait(26, [], 1, 10) = 0
> > [pid 534983]      0.010082 read(24,
> >
> > That makes mlx5 rx interrupts unusable for an application that does
> > more than just polling one rxq.
> 
> Excuse me, I don't understand this trace.
> What is the first read?
> Having a second read after epoll_wait is normal if a packet is received, isn't it?
>