Re: RFC: using NIC DMA ring as tracing buffer?

Hi Mathieu,

On Tue, Apr 16, 2024 at 10:49=E2=80=AFAM Mathieu Desnoyers
<[email protected]> wrote:
>
> On 2024-04-16 10:41, Alexander Aring wrote:
> > Hi all,
> >
> > I have an idea about using the DMA rings of a networking card as a
> > tracing buffer.
>
> The first thing I'd be worried about is overhead caused by
> false-sharing if you trace a large SMP/many-core system all
> into the same global NIC buffer. The cache lines will bounce
> left and right which is bad performance-wise.
>

modern NICs have several tx and rx dma rings. There is an ethtool
command to query the number:

sudo ethtool -g $IFACE

so it depends on the hardware if you can pin one or more rings on a
per-cpu buffer basis.

I hope that somehow helps to make this idea less worrisome.

Thanks.

- Alex