Re: [PATCH] rt-numa: optionally ignore runtime cpumask

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Jan 24, 2022 at 06:07:37PM +0100, Sebastian Andrzej Siewior wrote:
> On 2022-01-24 13:40:49 [-0300], Marcelo Tosatti wrote:
> > > Uses the $CPU (mask) specified. If $CPU is not part of the current CPU
> > > mask, why shouldn't it work?
> > 
> >        -a, --affinity[=PROC-SET]
> >               Run threads on the set of processors given by PROC-SET.  If PROC-SET is not specified, all processors will be used.  Threads will be assigned to processors
> >               in the set in numeric order, in a round-robin fashion.
> >               The set of processors can be specified as A,B,C, or A-C, or A-B,D-F, and so on*.  The ! character can be used to negate a set.  For example, !B-D means to
> >               use all available CPUs except B through D.  The cpu numbers are the same as shown in the processor field in /proc/cpuinfo.  See numa(3) for more
> >               information on specifying CPU sets.  * Support for CPU sets requires libnuma version >= 2.  For libnuma v1, PROC-SET, if specified, must be a single CPU
> >               number.
> > 
> > 
> > /*
> >  * After this function is called, affinity_mask is the intersection of
> >  * the user supplied affinity mask and the affinity mask from the run
> >  * time environment
> >  */
> > static void use_current_cpuset(int max_cpus, struct bitmask *cpumask)
> > {
> >         struct bitmask *curmask;
> >         int i;
> > 
> >         curmask = numa_allocate_cpumask();
> >         numa_sched_getaffinity(getpid(), curmask);
> > 
> >         /*
> >          * Clear bits that are not set in both the cpuset from the
> >          * environment, and in the user specified affinity.
> >          */
> >         for (i = 0; i < max_cpus; i++) {
> >                 if ((!numa_bitmask_isbitset(cpumask, i)) ||
> >                     (!numa_bitmask_isbitset(curmask, i)))
> >                         numa_bitmask_clearbit(cpumask, i);
> >         }
> > 
> >         numa_bitmask_free(curmask);
> > }
> > 
> > Consider 8 CPU system booted with isolcpus=3-7, and execution of 
> > "cyclictest -a 3-7".
> > 
> > sched_getaffinity() returns mask with bits set for CPUs 0 and 1.
> > The user supplied mask has bits 3-7 set.
> > 
> > The intersection between the user supplied mask and the affinity mask
> > from the run time environment has no bits set.
> 
> Okay. But does this make to keep? I understand that the current CPU-mask
> needs to be kept for masks like !B or !B-D. But is there a need to use
> the current CPU-mask when a specific mask has been specified by the user?

Ok, then:

1) If user specifies -a CPULIST, ignore sched_getaffinity().

2) If user specifies -a, or -a !CPULIST, use sched_getaffinity().

Will send a patch.