Large interruptions for EAL thread running on isol core

[Kinsella, Ray]

Have you tried testing with Jitter?

Looking through the CSIT data, will give an idea of the reasonable ranges for results.

Intel ICELAKE
https://docs.fd.io/csit/master/report/introduction/test_environment_sut_calib_icx.html

Intel CASCADE LAKE
https://docs.fd.io/csit/master/report/introduction/test_environment_sut_calib_clx.html

Ray K

-----Original Message-----
From: Antonio Di Bacco <a.dibacco.ks at gmail.com> 
Sent: Friday 24 June 2022 10:45
To: Stephen Hemminger <stephen at networkplumber.org>
Cc: users at dpdk.org
Subject: Re: Large interruptions for EAL thread running on isol core

Thank you, didn't know that "System management units" could steal CPU!!! That is scary

On Thu, Jun 23, 2022 at 8:42 PM Stephen Hemminger <stephen at networkplumber.org> wrote:
>
> On Thu, 23 Jun 2022 20:03:02 +0200
> Antonio Di Bacco <a.dibacco.ks at gmail.com> wrote:
>
> > I'm running a DPDK thread on an isolated core. I also set some  
> > flags that could help keeping the core at rest on linux like: 
> > nosoftlockup nohz_full rcu_nocbs irqaffinity.
> >
> > Unfortunately the thread gets some interruptions that stop the 
> > thread for about 20-30 micro seconds. This seems smal but my 
> > application suffers a lot.
> >
> > I also tried to use  rte_thread_set_priority that indeed has a 
> > strong effect but unfortunately creates problems to Linux (like 
> > network not working).
> >
> > Is there any other knob that could help running the DPDK thread with 
> > minimum or no interruptions at all?
>
> Look with perf and see what is happening.
> First check for interrupt affinity.
> Don't try real time priority.
>
> The other thing to look for would be any BIOS settings.
> Some system management units can take away CPU silently for polling 
> some internal housekeeping.