On 11/26/25 9:13 AM, Michal Koutný wrote:
On Mon, Nov 24, 2025 at 05:30:47PM -0500, Waiman Long <[email protected]> wrote:
In the example above, the final configuration is A1:0-1 & B1:1-2. As the cpu
lists overlap, we can't have both of them as valid partition roots. So
either one of A1 or B1 is valid or they are both invalid. The current code
makes them both invalid no matter the operation ordering. This patch will
make one of them valid given the operation ordering above. To minimize
partition invalidation, we will have to live with the fact that it will be
first-come first-serve as noted by Michal. I am not against this, we just
have to document it. However, the following operation order will still make
both of them invalid:
I'm skeptical of the FCFS behavior since I'm afraid it may be subject to
race conditions in practice.
BTW should cpuset.cpus and cpuset.cpus.exclusive have different behavior
in this regard?
Modification to cpumasks are all serialized by the cpuset_mutex. If you
are referring to 2 or more tasks doing parallel updates to various
cpuset control files of sibling cpusets, the results can actually vary
depending on the actual serialization results of those operations.
One difference between cpuset.cpus and cpuset.cpus.exclusive is the fact
that operations on cpuset.cpus.exclusive can fail if the result is not
exclusive WRT sibling cpusets, but becoming a valid partition is
guaranteed unless none of the exclusive CPUs are passed down from the
parent. The use of cpuset.cpus.exclusive is required for creating remote
partition.
OTOH, changes to cpuset.cpus will never fail, but becoming a valid
partition root is not guaranteed and is limited to the creation of local
partition only.
Does that answer your question?
Cheers,
Longman
