From a9e3760b0838299649c0d57cca44daaf40ba3c33 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 14 Sep 2026 22:12:34 -1000 Subject: sched_ext: Maintain an online cid mask in the scheduler arena Schedulers on the default cid mapping treat [0, nr_online_cids) as the online set and restart on hotplug. Schedulers that install their own mapping with scx_bpf_cid_override() have no way to learn which cids are online: the count no longer identifies members and the CPU-form cpumask is unusable from cid programs. This is an obvious hole in the cid API. Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's arena, allocated alongside the per-CPU scratch masks and populated after the cid mapping is finalized and before ops.init(), for child schedulers too. The pointer stays valid through ops.exit() with no reference to take. It is the arena offset as a void pointer, the same form struct_ops arena arguments arrive in. The verifier types the void return as a scalar for the program's arena cast. The mask follows the SCX hotplug notifications: seeded from cpu_active_mask and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask only inside a hotplug transition. Updates walk the scheduler list under the lock that also serializes unlinking. Reads are live, not atomic snapshots. Root initialization excludes hotplug. v2: Reworded the getter kerneldoc (Andrea Righi). Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- include/drm/intel/pick.h | 51 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 include/drm/intel/pick.h (limited to 'include/drm/intel/pick.h') diff --git a/include/drm/intel/pick.h b/include/drm/intel/pick.h new file mode 100644 index 000000000..d976fab8f --- /dev/null +++ b/include/drm/intel/pick.h @@ -0,0 +1,51 @@ +/* SPDX-License-Identifier: MIT */ +/* Copyright © 2026 Intel Corporation */ + +#ifndef _PICK_H_ +#define _PICK_H_ + +/* + * Given the first two numbers __a and __b of arbitrarily many evenly spaced + * numbers, pick the 0-based __index'th value. + * + * Always prefer this over _PICK() if the numbers are evenly spaced. + */ +#define _PICK_EVEN(__index, __a, __b) ((__a) + (__index) * ((__b) - (__a))) + +/* + * Like _PICK_EVEN(), but supports 2 ranges of evenly spaced address offsets. + * @__c_index corresponds to the index in which the second range starts to be + * used. Using math interval notation, the first range is used for indexes [ 0, + * @__c_index), while the second range is used for [ @__c_index, ... ). Example: + * + * #define _FOO_A 0xf000 + * #define _FOO_B 0xf004 + * #define _FOO_C 0xf008 + * #define _SUPER_FOO_A 0xa000 + * #define _SUPER_FOO_B 0xa100 + * #define FOO(x) _MMIO(_PICK_EVEN_2RANGES(x, 3, \ + * _FOO_A, _FOO_B, \ + * _SUPER_FOO_A, _SUPER_FOO_B)) + * + * This expands to: + * 0: 0xf000, + * 1: 0xf004, + * 2: 0xf008, + * 3: 0xa000, + * 4: 0xa100, + * 5: 0xa200, + * ... + */ +#define _PICK_EVEN_2RANGES(__index, __c_index, __a, __b, __c, __d) \ + (BUILD_BUG_ON_ZERO(!__is_constexpr(__c_index)) + \ + ((__index) < (__c_index) ? _PICK_EVEN(__index, __a, __b) : \ + _PICK_EVEN((__index) - (__c_index), __c, __d))) + +/* + * Given the arbitrary numbers in varargs, pick the 0-based __index'th number. + * + * Always prefer _PICK_EVEN() over this if the numbers are evenly spaced. + */ +#define _PICK(__index, ...) (((const u32 []){ __VA_ARGS__ })[__index]) + +#endif -- cgit v1.3.1