[PATCH 01/15] sched_ext: Pack scx_ent_flags' multi-bit fields at the top
From: Tejun Heo
Date: Fri Oct 23 2026 - 01:27:18 EST
The following patches add a flag for a kernel-owned slice to scx_ent_flags.
The two 3-bit fields, the task state at bits 8 to 10 and the reenqueue
reason at bits 12 to 14, sit right above the single-bit flags, so the new
flag would have to take bit 11 or 15, out of sequence with the rest.
Pack the fields at the top of the word, below SCX_TASK_CURSOR, the state at
bits 25 to 27 and the reason at bits 28 to 30, so that the single-bit flags
continue from bit 8.
The renumbering changes the values a BPF scheduler reads from p->scx.flags.
Nothing in the kernel or the in-tree schedulers hardcodes the numbers. The
enum ABI table in tools/sched_ext/include/scx/enums_abi.autogen.h, kept for
repairing enum values that a kernel's BTF truncates, is regenerated for the
two fields. In the scx repository, scx_eevdf tests SCX_TASK_REENQ_IMMED and
SCX_TASK_REENQ_PREEMPTED against SCX_TASK_REENQ_REASON_MASK. Those three
names belong in its load-time enum table, so that they follow the running
kernel. No behavior change.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
include/linux/sched/ext.h | 11 +++++---
.../sched_ext/include/scx/enums_abi.autogen.h | 28 +++++++++----------
2 files changed, 21 insertions(+), 18 deletions(-)
diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index efd635a99309..b341c328948e 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -107,7 +107,10 @@ enum scx_ent_flags {
SCX_TASK_RUN_TRACKED = 1 << 7, /* task is in an ops.running()/stopping() session */
/*
- * Bits 8 to 10 are used to carry task state:
+ * The multi-bit fields are packed at the top, below SCX_TASK_CURSOR, so
+ * that the single-bit flags stay contiguous from bit 0.
+ *
+ * Bits 25 to 27 are used to carry task state:
*
* NONE ops.init_task() not called yet
* INIT_BEGIN ops.init_task() in flight; see sched_ext_dead()
@@ -116,7 +119,7 @@ enum scx_ent_flags {
* ENABLED fully initialized and in sched_ext
* DEAD terminal state set by sched_ext_dead()
*/
- SCX_TASK_STATE_SHIFT = 8,
+ SCX_TASK_STATE_SHIFT = 25,
SCX_TASK_STATE_BITS = 3,
SCX_TASK_STATE_MASK = ((1 << SCX_TASK_STATE_BITS) - 1) << SCX_TASK_STATE_SHIFT,
@@ -128,7 +131,7 @@ enum scx_ent_flags {
SCX_TASK_DEAD = 5 << SCX_TASK_STATE_SHIFT,
/*
- * Bits 12 to 14 are used to carry reenqueue reason. In addition to
+ * Bits 28 to 30 are used to carry reenqueue reason. In addition to
* %SCX_ENQ_REENQ flag, ops.enqueue() can also test for
* %SCX_TASK_REENQ_REASON_NONE to distinguish reenqueues.
*
@@ -139,7 +142,7 @@ enum scx_ent_flags {
* CAP sub-sched cap miss, see p->scx.reenq_reason_*
* PROXY proxy state prevented a remote DSQ transfer
*/
- SCX_TASK_REENQ_REASON_SHIFT = 12,
+ SCX_TASK_REENQ_REASON_SHIFT = 28,
SCX_TASK_REENQ_REASON_BITS = 3,
SCX_TASK_REENQ_REASON_MASK = ((1 << SCX_TASK_REENQ_REASON_BITS) - 1) << SCX_TASK_REENQ_REASON_SHIFT,
diff --git a/tools/sched_ext/include/scx/enums_abi.autogen.h b/tools/sched_ext/include/scx/enums_abi.autogen.h
index 1186daa9cb14..05a460611c4d 100644
--- a/tools/sched_ext/include/scx/enums_abi.autogen.h
+++ b/tools/sched_ext/include/scx/enums_abi.autogen.h
@@ -120,24 +120,24 @@ static const struct __scx_enum_abi_val __scx_enum_abi_vals[]
{ "scx_ent_flags", "SCX_TASK_IMMED", 0x20LLU },
{ "scx_ent_flags", "SCX_TASK_PROTECTED", 0x40LLU },
{ "scx_ent_flags", "SCX_TASK_RUN_TRACKED", 0x80LLU },
- { "scx_ent_flags", "SCX_TASK_STATE_SHIFT", 0x8LLU },
+ { "scx_ent_flags", "SCX_TASK_STATE_SHIFT", 0x19LLU },
{ "scx_ent_flags", "SCX_TASK_STATE_BITS", 0x3LLU },
- { "scx_ent_flags", "SCX_TASK_STATE_MASK", 0x700LLU },
+ { "scx_ent_flags", "SCX_TASK_STATE_MASK", 0xe000000LLU },
{ "scx_ent_flags", "SCX_TASK_NONE", 0x0LLU },
- { "scx_ent_flags", "SCX_TASK_INIT_BEGIN", 0x100LLU },
- { "scx_ent_flags", "SCX_TASK_INIT", 0x200LLU },
- { "scx_ent_flags", "SCX_TASK_READY", 0x300LLU },
- { "scx_ent_flags", "SCX_TASK_ENABLED", 0x400LLU },
- { "scx_ent_flags", "SCX_TASK_DEAD", 0x500LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_REASON_SHIFT", 0xcLLU },
+ { "scx_ent_flags", "SCX_TASK_INIT_BEGIN", 0x2000000LLU },
+ { "scx_ent_flags", "SCX_TASK_INIT", 0x4000000LLU },
+ { "scx_ent_flags", "SCX_TASK_READY", 0x6000000LLU },
+ { "scx_ent_flags", "SCX_TASK_ENABLED", 0x8000000LLU },
+ { "scx_ent_flags", "SCX_TASK_DEAD", 0xa000000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_REASON_SHIFT", 0x1cLLU },
{ "scx_ent_flags", "SCX_TASK_REENQ_REASON_BITS", 0x3LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_REASON_MASK", 0x7000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_REASON_MASK", 0x70000000LLU },
{ "scx_ent_flags", "SCX_TASK_REENQ_NONE", 0x0LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_KFUNC", 0x1000LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_IMMED", 0x2000LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_PREEMPTED", 0x3000LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_CAP", 0x4000LLU },
- { "scx_ent_flags", "SCX_TASK_REENQ_PROXY", 0x5000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_KFUNC", 0x10000000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_IMMED", 0x20000000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_PREEMPTED", 0x30000000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_CAP", 0x40000000LLU },
+ { "scx_ent_flags", "SCX_TASK_REENQ_PROXY", 0x50000000LLU },
{ "scx_ent_flags", "SCX_TASK_CURSOR", 0xffffffff80000000LLU },
{ "scx_exit_code", "SCX_ECODE_RSN_HOTPLUG", 0x100000000LLU },
{ "scx_exit_code", "SCX_ECODE_RSN_CGROUP_OFFLINE", 0x200000000LLU },
--
2.56.0