On 09/06/2018 05:20 PM, Waiman Long wrote: > On 08/27/2018 01:50 PM, Waiman Long wrote: >> On 08/27/2018 12:40 PM, Tejun Heo wrote: >>> Hello, Waiman. >>> >>> On Mon, Aug 27, 2018 at 10:41:24AM -0400, Waiman Long wrote: >>>> Cpuset allows arbitrary modification of cpu list in "cpuset.cpus" >>>> even if the requested CPUs won't be granted in "cpuset.cpus.effective" >>>> as restricted by its parent. However, the validate_change() function >>>> will inhibit removal of CPUs that have been used in child cpusets. >>>> >>>> Being a partition root, however, limits the kind of cpu list >>>> modification that is allowed. Adding CPUs is not allowed if the new >>>> CPUs are not in the parent's effective cpu list that can be put into >>>> "cpuset.cpus.reserved". In addition, a child partition cannot exhaust >>>> all the parent's effective CPUs. >>>> >>>> Because of the implicit cpu exclusive nature of the partition root, >>>> cpu changes that break that cpu exclusivity will not be allowed. Other >>>> changes that break the conditions of being a partition root is generally >>>> allowed. However, the partition flag of the cpuset as well those of >>>> the descendant partitions will be forcefully turned off. >>> First of all, thanks a lot for your persistence. I'm not necessarily >>> against the flag being forced off but wonder whether the same >>> config/effective approach can be used as in .cpus and .mems. Can you >>> elaborate a bit on the choice here? >>> >>> Thank you. >> My current code has explicitly assumed the following relationship for >> partition root. >> >> cpus_allowed = effective_cpus + reserved_cpus >> >> Also effective_cpus cannot be empty. Specifically, cpus_allowed has to >> be equal to effective_cpus before a cpuset can be made a partition root. >> >> Any changes that break the above conditions will turn off the partition >> flag forcefully. The only exception is cpu offlining where cpus_allowed >>> effective_cpus + reserved_cpus can happen. >> One reason for doing so is because reserved_cpus is hidden. So the main >> way to infer that is to do cpus_allowed - effective_cpus. >> >> It is probably doable to make cpus_allowed >= effective_cpus + >> reserved_cpus in general, but we may need to expose reserved_cpus as a >> read-only file, for instance. There may also be other complications that >> we will need to take care of if this is supported. My current preference >> is to not doing that unless there is compelling reason to do so. >> >> Cheers, >> Longman > For the current patch, one of conditions to allow users to turn on the > partition flag is cpus_allowed = effective_cpus. Once the partition flag > is on, the twos have to be the same too except with cpu offlining. This > patch is added to allow arbitrary modification to the cpuset.cpus file > except those that have already been forbidden in the existing code. When > the modification violates the rules of being a partition root, the flag > will be turned off or we will have to deny the modification request. > > I am admitting that it is an easy way out in term of programming effort > as I am not sure how much effort is needed to enable arbitrary > modification to cpuset.cpus without force disabling and whether such an > effort is even worthwhile to do. > > We can certainly relax the current restrictions in the future. Any > suggestion to improve the patchset is welcome. I would really like to > see this merged in 4.20 (or maybe 5.0) kernel. > > Cheers, > Longman > Tejun,
Sorry for bothering you again. I would like to know your assessment of this patchset as to whether it is ready or not. Thanks, Longman
