> From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
> Sent: Thursday, 6 October 2022 10.59
>
> On 2022-10-06 10:18, Morten Brørup wrote:
> >> From: Mattias Rönnblom [mailto:mattias.ronnblom@ericsson.com]
> >> Sent: Thursday, 6 October 2022 09.51
> >>
> >> On 2022-10-06 08:53, Morten Brørup wrote:
> >
> > [...]
> >
> >>> I have been wondering how accurate the tests really are. Where can
> I
> >> see what is being done to ensure that the EAL worker threads are
> fully
> >> isolated, and never interrupted by the O/S scheduler or similar?
> >>>
> >>
> >> There are kernel-level counters for how many times a thread have
> been
> >> involuntarily interrupted,
> >
> > Thanks, Mattias. I will look into that.
> >
> > Old kernels (2.4 and 2.6) ascribed the time spent in interrupt
> handlers to the CPU usage of the running process, instead of counting
> the time spent in interrupt handlers separately. Does anyone know it
> this has been fixed?
> >
>
> If you mean top half interrupt handler, my guess would be it does not
> matter, except in some strange corner cases or faulty hardware. An ISR
> should have very short run time, and not being run *that* often (after
> NAPI). With isolated cores, it should be even less of a problem, but
> then you may not have that.
>

Many years ago, we used a NIC that didn't have DMA, and only 4 RX descriptors, so it had to be serviced in the top half.

> Bottom halves are not attributed to the process, I believe.

This is an improvement.

> (In old
> kernels, the time spent in soft IRQs were not attributed to anything,
> which could create situations where the system was very busy indeed
> [e.g., with network stack bottom halves doing IP forwarding], but
> looking idle in 'top'.)

We also experienced that. The kernel's scheduling information was completely useless, so eventually we removed the CPU Utilization information from our GUI. ;-)

And IIRC, it wasn't fixed in kernel 2.6.

>
> >> and also, if I recall correctly, the amount
> >> of wall-time the thread have been runnable, but not running (i.e.,
> >> waiting to be scheduled). The latter may require some scheduler
> debug
> >> kernel option being enabled on the kernel build.
> >
> >