Re: AMD EPYC virtual network performances

[Jürgen Groß <jgross@xxxxxxxx>]

On 14.08.24 00:36, Elliott Mitchell wrote:
> On Tue, Aug 13, 2024 at 08:55:42PM +0200, Jürgen Groß wrote:
> > On 13.08.24 19:49, Elliott Mitchell wrote:
> > > On Tue, Aug 13, 2024 at 01:16:06PM +0200, Jürgen Groß wrote:
> > > > I don't see a connection here, as spurious interrupts (as seen by the
> > > > hypervisor in your case) and spurious events (as seen by Andrei) are
> > > > completely different (hardware vs. software level).
> > > The entries seem to appear at an average of about 1/hour.  Could be most
> > > events are being dropped and 10x that number are occuring.  If so, those
> > > extras could be turning into spurious events seen by various domains.
> > Even 10 spurious events per hour should not have a measurable impact
> > on performance.
> Come to think of it, depending upon time that domain is sometimes low
> activity (build so it is either pegging or idle).  The 1/hour was during
> idle times, so during busy times it might be much worse.  I haven't been
> tracking `xl dmesg` as carefully recently.
>
> Do the maintainers ever run machines with "iommu=debug"?  I'm actually
> rather concerned *anything* spurious is showing up as I'm left suspecting
> there may have been something lurking for some time.
>
> > > There is a possibility spurious interrupts are being turned into spurious
> > > events by the back-end drivers.
> > No, I don't think so.
> >
> > > Jürgen Groß, what is the performance impact of "iommu=debug"?  Seems to
> > > mostly cause more reporting and have minimal/no performance effect.
> > I guess you are referring to the Xen option? I'm no expert in this
> > area.
> Drat.  I haven't noticed much, which would match with simply enabling a
> bunch of debugging printk()s (alas I'm not monitoring performance closely
> enough to be sure).  Guess I wait for Andrei Semenov to state a comfort
> level with trying "iommu=debug".
You didn't answer my question.

Please send the Xen and dom0 command line options you are using.


Juergen