Re: [PATCH v3 1/2] eal: get/set thread priority per thread identifier

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 25 May 2022 23:29:57 -0700
Tyler Retzlaff <roretzla@linux.microsoft.com> wrote:

> On Tue, May 24, 2022 at 07:51:05AM -0700, Stephen Hemminger wrote:
> > On Tue, 24 May 2022 04:08:36 -0700
> > Tyler Retzlaff <roretzla@linux.microsoft.com> wrote:
> >   
> > > +static int
> > > +thread_map_priority_to_os_value(enum rte_thread_priority eal_pri,
> > > +		int *os_pri, int *pol)
> > > +{
> > > +	/* Clear the output parameters */
> > > +	*os_pri = sched_get_priority_min(SCHED_OTHER) - 1;
> > > +	*pol = -1;
> > > +
> > > +	switch (eal_pri) {
> > > +	case RTE_THREAD_PRIORITY_NORMAL:
> > > +		*pol = SCHED_OTHER;
> > > +
> > > +		/*
> > > +		 * Choose the middle of the range to represent
> > > +		 * the priority 'normal'.
> > > +		 * On Linux, this should be 0, since both
> > > +		 * sched_get_priority_min/_max return 0 for SCHED_OTHER.
> > > +		 */
> > > +		*os_pri = (sched_get_priority_min(SCHED_OTHER) +
> > > +			sched_get_priority_max(SCHED_OTHER))/2;
> > > +		break;
> > > +	case RTE_THREAD_PRIORITY_REALTIME_CRITICAL:
> > > +		*pol = SCHED_RR;
> > > +		*os_pri = sched_get_priority_max(SCHED_RR);
> > > +		break;  
> > 
> > Many people have experimented with realtime priorities with DPDK
> > and Linux, and have never heard of any one not having problems.
> > 
> > Recommend that this either be an error add a warning log message
> > that "Setting real time priority may break"  
> 
> so i went back through the feedback when the priority change was
> originally introduced. you're request was that you didn't want it to be
> possible for realtime priority to be set on linux.
> 
> this particular function is just about mapping the abstracted
> representation of realtime priority in eal to the platform specific
> linux representation.
> 
> so if you take a look at the other parts of the patch you will notice
> that the rte_thread_set_priority() for linux will in fact fail if you
> try to use realtime priority.
> 
> additionally, the unit test exercises that attempting to use realtime
> priority does fail for linux.
> 
> take another look and let me know if you don't agree.
> 
> thanks


Thanks for clarifying.
Is there any analog for SCHED_DEADLINE worth considering?

Acked-by: Stephen Hemminger <stephen@networkplumber.org>