Messages in this thread | | | Date | Wed, 1 Feb 2023 10:03:27 -0500 | Subject | Re: [PATCH 2/2] cpuset: Call set_cpus_allowed_ptr() with appropriate mask for task | From | Waiman Long <> |
| |
On 2/1/23 04:15, Peter Zijlstra wrote: > On Tue, Jan 31, 2023 at 09:22:44PM -0500, Waiman Long wrote: >> On 1/31/23 17:17, Will Deacon wrote: >>> set_cpus_allowed_ptr() will fail with -EINVAL if the requested >>> affinity mask is not a subset of the task_cpu_possible_mask() for the >>> task being updated. Consequently, on a heterogeneous system with cpusets >>> spanning the different CPU types, updates to the cgroup hierarchy can >>> silently fail to update task affinities when the effective affinity >>> mask for the cpuset is expanded. >>> >>> For example, consider an arm64 system with 4 CPUs, where CPUs 2-3 are >>> the only cores capable of executing 32-bit tasks. Attaching a 32-bit >>> task to a cpuset containing CPUs 0-2 will correctly affine the task to >>> CPU 2. Extending the cpuset to CPUs 0-3, however, will fail to extend >>> the affinity mask of the 32-bit task because update_tasks_cpumask() will >>> pass the full 0-3 mask to set_cpus_allowed_ptr(). >>> >>> Extend update_tasks_cpumask() to take a temporary 'cpumask' paramater >>> and use it to mask the 'effective_cpus' mask with the possible mask for >>> each task being updated. >>> >>> Fixes: 431c69fac05b ("cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()") >>> Signed-off-by: Will Deacon <will@kernel.org> >>> --- >>> >>> Note: We wondered whether it was worth calling guarantee_online_cpus() >>> if the cpumask_and() returns 0 in update_tasks_cpumask(), but given that >>> this path is only called when the effective mask changes, it didn't >>> seem appropriate. Ultimately, if you have 32-bit tasks attached to a >>> cpuset containing only 64-bit cpus, then the affinity is going to be >>> forced. >> Now I see how the sched_setaffinity() change is impacting arm64. Instead of >> putting in the bandage in cpuset. I would suggest doing another cpu masking >> in __set_cpus_allowed_ptr() similar to what is now done for user_cpus_ptr. > NO! cpuset is *BROKEN* it has been for a while, it needs to get fixed. > > Masking the offline CPUs is *WRONG*. > This patch is not related to offline cpus at all. It is all about the 32-bit misfit cpus in some arm64 system.
Cheers, Longman
| |