On Mon, Jan 24, 2022 at 05:26:26PM +0100, Sebastian Andrzej Siewior wrote:
> On 2022-01-24 09:58:31 [-0300], Marcelo Tosatti wrote:
> > You mean "using all CPUs which are part of the current affinity mask by
> > default" ? (where current affinity mask would mean user specified CPU
> > mask).
> >
> > > And then either specify the
> > > requested CPU mask or use explicitly all CPUs.
> >
> > Do you mean to drop
> >
> > /*
> > * Clear bits that are not set in both the cpuset from the
> > * environment, and in the user specified affinity.
> >
> > And just attempt to use the user specified mask? (which will then return
> > failure to the user in which case he can correct it).
> >
> After reading it again, I don't get it.
> cyclictest -a
>
> Uses all CPUs in the system.
>
> cyclictest -a $CPU
>
> 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.
