On 7/10/23 21:00, Tejun Heo wrote:
Hello,
On Mon, Jul 10, 2023 at 08:33:11PM -0400, Waiman Long wrote:
I would like to clarify that withdrawal of CPUs from cpuset.cpus.exclusive is always allowed. It is the addition of CPUs not presents in cpuset.cpus that will be rejected. The invariant is that cpuset.cpus.exclusive must always be a subset of cpuset.cpus. Any change that violates this rule is not allowed. Alternately I can silently dropped the offending CPUs without returning an error, but that may surprise users.
Right, that'd be confusing.
BTW, withdrawal of CPUs from cpuset.cpus will also withdraw them from cpuset.cpus.exclusive, if present. This allows the partition code to use cpuset.cpus.exclusive directly to determine the allowable exclusive CPUs without doing an intersection with cpuset.cpus each time it is used.
This is kinda confusing too, I think. Changing cpuset.cpus in an ancestor doesn't affect the contents of the descendants' cpuset.cpus files but would directly modify the contents of their cpuset.cpus.exclusive files.
There's some inherent friction because cpuset.cpus separates configuration (cpuset.cpus) and the current state (cpuset.cpus.effective) while cpuset.cpus.exclusive is trying to do both in the same interface file. When the two behavior modes collide, it becomes rather confusing. Do you think it'd make sense to make cpus.exclusive follow the same pattern as cpuset.cpus?
I don't want to add another cpuset.cpus.exclusive.effective control file. One possibility is to keep another effective masks in the struct cpuset and list both exclusive cpus set by the user and the effective ones side by side, like "<cpus> (<effective_cpus>)" if they differ or some other format. What do you think?
Regards, Longman