cpuclass: hint all good CPU sets instead of only the best#719
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Satisfying CPU affinity to multiple preferences encoded in preferCloseToDevice requires more flexibility than provided in CPU class preference. For example, a container requires PCT HP (high priority) CPUs and CPU affinity to a GPU device. There are enough HP CPUs available in both sockets. Because socket 0 happens to have fewer HP CPUs available, cpuclass hint considers it worse choice than socket 1 with more HP CPUs. However, the GPU may be connected to socket 0. As a result, preferCloseToDevices consists of a GPU-affinity hint to all CPUs on socket 0, and HP CPU affinity hint to HP CPUs on socket 1. The latter hint will be ignored, in which order they ever happen to be. This commit changes cpuclass (HP CPUs) hints so that all good-enough CPU sets will be published. Given that cpuclass hints are applied after device (GPU) hints, above example works as follows. GPU-affinity hints all CPUs on socket 0. Next, best HP CPU affinity would hint HP CPUs on socket 1. As the intersection hinted CPUs is empty, cputree.go allocator ignores this hint. Finally, second-best HP CPU affinity hints HP CPUs on socket 0. Now intersection with already taken hints is not empty, so this hint is applied, and the container will get HP CPUs near the GPU. Technically, this commit changes CPU class AllocationHints to contain best-first-ordered list of good-enough CPU sets as alternatives for CPU allocators to prefer. Signed-off-by: Antti Kervinen <antti.kervinen@intel.com>
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Satisfying CPU affinity to multiple preferences encoded in preferCloseToDevice requires more flexibility than provided in CPU class preference.
For example, a container requires PCT HP (high priority) CPUs and CPU affinity to a GPU device. There are enough HP CPUs available in both sockets. Because socket 0 happens to have fewer HP CPUs available, cpuclass hint considers it worse choice than socket 1 with more HP CPUs. However, the GPU may be connected to socket 0. As a result, preferCloseToDevices consists of a GPU-affinity hint to all CPUs on socket 0, and HP CPU affinity hint to HP CPUs on socket 1. The latter hint will be ignored, in which order they ever happen to be.
This commit changes cpuclass (HP CPUs) hints so that all good-enough CPU sets will be published. Given that cpuclass hints are applied after device (GPU) hints, above example works as follows. GPU-affinity hints all CPUs on socket 0. Next, best HP CPU affinity would hint HP CPUs on socket 1. As the intersection hinted CPUs is empty, cputree.go allocator ignores this hint. Finally, second-best HP CPU affinity hints HP CPUs on socket 0. Now intersection with already taken hints is not empty, so this hint is applied, and the container will get HP CPUs near the GPU.
Technically, this commit changes CPU class AllocationHints to contain best-first-ordered list of good-enough CPU sets as alternatives for CPU allocators to prefer.