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From: Thomas Monjalon <thomas@monjalon.net>
To: Bruce Richardson <bruce.richardson@intel.com>,
 Tyler Retzlaff <roretzla@linux.microsoft.com>
Cc: dev@dpdk.org, Morten =?ISO-8859-1?Q?Br=F8rup?= <mb@smartsharesystems.com>, 
 Stephen Hemminger <stephen@networkplumber.org>,
 Min Zhou <zhoumin@loongson.cn>, stable@dpdk.org, dev@dpdk.org,
 David Marchand <david.marchand@redhat.com>,
 Anatoly Burakov <anatoly.burakov@intel.com>,
 Narcisa Vasile <navasile@linux.microsoft.com>,
 Tyler Retzlaff <roretzla@linux.microsoft.com>,
 Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>,
 Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>,
 Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Subject: Re: [PATCH] eal/unix: allow creating thread with real-time priority
Date: Wed, 25 Oct 2023 15:44:25 +0200
Message-ID: <3187925.5fSG56mABF@thomas>
In-Reply-To: <ZTkZUKMbLs06MY2N@bricha3-MOBL.ger.corp.intel.com>
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Errors-To: stable-bounces@dpdk.org

25/10/2023 15:34, Bruce Richardson:
> On Wed, Oct 25, 2023 at 03:15:49PM +0200, Thomas Monjalon wrote:
> > 24/10/2023 18:04, Stephen Hemminger:
> > > On Tue, 24 Oct 2023 15:55:13 +0200
> > > Morten Br=F8rup <mb@smartsharesystems.com> wrote:
> > >=20
> > > > >=20
> > > > >    4. It MAY be used by preemptible multi-producer and/or preempt=
ible multi-
> > > > > consumer pthreads whose scheduling policy are all SCHED_OTHER(cfs=
), SCHED_IDLE
> > > > > or SCHED_BATCH. User SHOULD be aware of the performance penalty b=
efore using
> > > > > it.
> > > > >=20
> > > > > -  5. It MUST not be used by multi-producer/consumer pthreads, wh=
ose
> > > > > scheduling policies are SCHED_FIFO or SCHED_RR.
> > > > > +  5. It MUST not be used by multi-producer/consumer pthreads
> > > > > +     whose scheduling policies are ``SCHED_FIFO``
> > > > > +     or ``SCHED_RR`` (``RTE_THREAD_PRIORITY_REALTIME_CRITICAL``)=
=2E =20
> > > >=20
> > > > Do the RTS or HTS ring modes make any difference here?
> > > >=20
> > > > Anyway, I agree that real-time priority should not be forbidden on =
Unix.
> > > >=20
> > > > Acked-by: Morten Br=F8rup <mb@smartsharesystems.com>
> > >=20
> > > Please add a big warning message in the rte_thread.c and the document=
ation
> > > to describe the problem. Need to have the "you have been warned" acti=
on.
> >=20
> > Yes I can add more warnings.
> >=20
> > > Use of RT priority is incompatible with 100% poll mode as is typicall=
y done
> > > in DPDK applications. A real time thread has higher priority than oth=
er necessary
> > > kernel threads on the same CPU. Therefore if the RT thread never slee=
ps, critical
> > > system actions such as delayed writes, network packet processing and =
timer updates
> > > will not happen which makes the system unstable.
> >=20
> > Yes, and it is shown by the test on loongarch:
> > DPDK:fast-tests / threads_autotest        TIMEOUT        80.01s
> > http://mails.dpdk.org/archives/test-report/2023-October/488760.html
> >=20
> > I'll try to pass the test by adding a sleep in the test thread.
> >=20
>=20
> "sched_yield()" rather than sleep perhaps? Might better convey the
> intention of the call.

Do we have sched_yield on Windows?