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Caps are per-cid permissions parents delegate to direct children via scx_bpf_sub_grant() / scx_bpf_sub_revoke(). A child's cap set is always a subset of its parent's. Sub-scheds check their caps locally, and cross-sched communication is needed only when the delegation set itself changes. Caps will be used to implement sub-sched scheduling on the enqueue path. Picking a cid for a task at a leaf depends on which cids the leaf is allowed to use, and resolving that programmatically on every enqueue would mean a cross-sched round-trip call chain, possibly retrying if the request can't be granted as-is. The dispatch path is different - it runs as top-down recursion via scx_bpf_sub_dispatch(). Locking is per shard. cid space is split into shards, and each sub-sched has its own pshard->lock for each shard. Operations are broken up on shard boundaries. Different shards never contend. Shards are expected to be topology-aligned and likely to serve as the locality unit when cids are allocated to schedulers, so per-shard lock granularity scales naturally with the allocation pattern. This patch adds the framework with a single dummy cap. Real caps land in later patches. The enable path is reordered for pshards. scx_arena_pool_init() moves ahead of scx_link_sched() so the pshards are allocated before the sched becomes reachable - scx_alloc_pshards() skips allocation when the arena pool isn't initialized. - scx_bpf_sub_grant(): Per-cid all-or-nothing grant to direct child. - scx_bpf_sub_revoke(): Clear caps on @cmask across @child and its subtree. - scx_bpf_sub_caps(): Lockless snapshot of caps on a cid range. /sys/kernel/sched_ext/SCHED/caps shows the caps each scheduler currently holds. v4: Move the pshard[] full build/publish and the err_disable scx_error() recording to earlier patches. (sashiko AI) v3: Build pshard[] fully before publishing it, read it with READ_ONCE. (sashiko AI) v2: Validate ops before scx_link_sched() publishes the sub. (sashiko AI) Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Andrea Righi <arighi@nvidia.com> |
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