[PATCH 03/11] sched_ext: Make find_dsq_for_dispatch() handle SCX_DSQ_LOCAL_ON

Tejun Heo
2024-08-30T11:04:26Z

find_dsq_for_dispatch() handles all DSQ IDs except SCX_DSQ_LOCAL_ON.
Instead, each caller is hanlding SCX_DSQ_LOCAL_ON before calling it. Move
SCX_DSQ_LOCAL_ON lookup into find_dsq_for_dispatch() to remove duplicate
code in direct_dispatch() and dispatch_to_local_dsq().

No functional changes intended.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/sched/ext.c | 90 +++++++++++++++++++++-------------------------
1 file changed, 40 insertions(+), 50 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 3facfca73337..80387cd9b8c3 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1726,6 +1726,15 @@ static struct scx_dispatch_q *find_dsq_for_dispatch(struct rq *rq, u64 dsq_id,
if (dsq_id == SCX_DSQ_LOCAL)
return &rq->scx.local_dsq;

+ if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) {
+ s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK;
+
+ if (!ops_cpu_valid(cpu, "in SCX_DSQ_LOCAL_ON dispatch verdict"))
+ return &scx_dsq_global;
+
+ return &cpu_rq(cpu)->scx.local_dsq;
+ }
+
dsq = find_non_local_dsq(dsq_id);
if (unlikely(!dsq)) {
scx_ops_error("non-existent DSQ 0x%llx for %s[%d]",
@@ -1769,8 +1778,8 @@ static void mark_direct_dispatch(struct task_struct *ddsp_task,
static void direct_dispatch(struct task_struct *p, u64 enq_flags)
{
struct rq *rq = task_rq(p);
- struct scx_dispatch_q *dsq;
- u64 dsq_id = p->scx.ddsp_dsq_id;
+ struct scx_dispatch_q *dsq =
+ find_dsq_for_dispatch(rq, p->scx.ddsp_dsq_id, p);

touch_core_sched_dispatch(rq, p);

@@ -1782,15 +1791,9 @@ static void direct_dispatch(struct task_struct *p, u64 enq_flags)
* DSQ_LOCAL_ON verdicts targeting the local DSQ of a remote CPU, defer
* the enqueue so that it's executed when @rq can be unlocked.
*/
- if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) {
- s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK;
+ if (dsq->id == SCX_DSQ_LOCAL && dsq != &rq->scx.local_dsq) {
unsigned long opss;

- if (cpu == cpu_of(rq)) {
- dsq_id = SCX_DSQ_LOCAL;
- goto dispatch;
- }
-
opss = atomic_long_read(&p->scx.ops_state) & SCX_OPSS_STATE_MASK;

switch (opss & SCX_OPSS_STATE_MASK) {
@@ -1817,8 +1820,6 @@ static void direct_dispatch(struct task_struct *p, u64 enq_flags)
return;
}

-dispatch:
- dsq = find_dsq_for_dispatch(rq, dsq_id, p);
dispatch_enqueue(dsq, p, p->scx.ddsp_enq_flags | SCX_ENQ_CLEAR_OPSS);
}

@@ -2303,51 +2304,38 @@ static bool consume_dispatch_q(struct rq *rq, struct scx_dispatch_q *dsq)
enum dispatch_to_local_dsq_ret {
DTL_DISPATCHED, /* successfully dispatched */
DTL_LOST, /* lost race to dequeue */
- DTL_NOT_LOCAL, /* destination is not a local DSQ */
DTL_INVALID, /* invalid local dsq_id */
};

/**
* dispatch_to_local_dsq - Dispatch a task to a local dsq
* @rq: current rq which is locked
- * @dsq_id: destination dsq ID
+ * @dst_dsq: destination DSQ
* @p: task to dispatch
* @enq_flags: %SCX_ENQ_*
*
- * We're holding @rq lock and want to dispatch @p to the local DSQ identified by
- * @dsq_id. This function performs all the synchronization dancing needed
- * because local DSQs are protected with rq locks.
+ * We're holding @rq lock and want to dispatch @p to @dst_dsq which is a local
+ * DSQ. This function performs all the synchronization dancing needed because
+ * local DSQs are protected with rq locks.
*
* The caller must have exclusive ownership of @p (e.g. through
* %SCX_OPSS_DISPATCHING).
*/
static enum dispatch_to_local_dsq_ret
-dispatch_to_local_dsq(struct rq *rq, u64 dsq_id, struct task_struct *p,
- u64 enq_flags)
+dispatch_to_local_dsq(struct rq *rq, struct scx_dispatch_q *dst_dsq,
+ struct task_struct *p, u64 enq_flags)
{
struct rq *src_rq = task_rq(p);
- struct rq *dst_rq;
+ struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq);

/*
* We're synchronized against dequeue through DISPATCHING. As @p can't
* be dequeued, its task_rq and cpus_allowed are stable too.
+ *
+ * If dispatching to @rq that @p is already on, no lock dancing needed.
*/
- if (dsq_id == SCX_DSQ_LOCAL) {
- dst_rq = rq;
- } else if ((dsq_id & SCX_DSQ_LOCAL_ON) == SCX_DSQ_LOCAL_ON) {
- s32 cpu = dsq_id & SCX_DSQ_LOCAL_CPU_MASK;
-
- if (!ops_cpu_valid(cpu, "in SCX_DSQ_LOCAL_ON dispatch verdict"))
- return DTL_INVALID;
- dst_rq = cpu_rq(cpu);
- } else {
- return DTL_NOT_LOCAL;
- }
-
- /* if dispatching to @rq that @p is already on, no lock dancing needed */
if (rq == src_rq && rq == dst_rq) {
- dispatch_enqueue(&dst_rq->scx.local_dsq, p,
- enq_flags | SCX_ENQ_CLEAR_OPSS);
+ dispatch_enqueue(dst_dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
return DTL_DISPATCHED;
}

@@ -2489,19 +2477,21 @@ static void finish_dispatch(struct rq *rq, struct task_struct *p,

BUG_ON(!(p->scx.flags & SCX_TASK_QUEUED));

- switch (dispatch_to_local_dsq(rq, dsq_id, p, enq_flags)) {
- case DTL_DISPATCHED:
- break;
- case DTL_LOST:
- break;
- case DTL_INVALID:
- dsq_id = SCX_DSQ_GLOBAL;
- fallthrough;
- case DTL_NOT_LOCAL:
- dsq = find_dsq_for_dispatch(cpu_rq(raw_smp_processor_id()),
- dsq_id, p);
+ dsq = find_dsq_for_dispatch(this_rq(), dsq_id, p);
+
+ if (dsq->id == SCX_DSQ_LOCAL) {
+ switch (dispatch_to_local_dsq(rq, dsq, p, enq_flags)) {
+ case DTL_DISPATCHED:
+ break;
+ case DTL_LOST:
+ break;
+ case DTL_INVALID:
+ dispatch_enqueue(&scx_dsq_global, p,
+ enq_flags | SCX_ENQ_CLEAR_OPSS);
+ break;
+ }
+ } else {
dispatch_enqueue(dsq, p, enq_flags | SCX_ENQ_CLEAR_OPSS);
- break;
}
}

@@ -2718,13 +2708,13 @@ static void process_ddsp_deferred_locals(struct rq *rq)
*/
while ((p = list_first_entry_or_null(&rq->scx.ddsp_deferred_locals,
struct task_struct, scx.dsq_list.node))) {
- s32 ret;
+ struct scx_dispatch_q *dsq;

list_del_init(&p->scx.dsq_list.node);

- ret = dispatch_to_local_dsq(rq, p->scx.ddsp_dsq_id, p,
- p->scx.ddsp_enq_flags);
- WARN_ON_ONCE(ret == DTL_NOT_LOCAL);
+ dsq = find_dsq_for_dispatch(rq, p->scx.ddsp_dsq_id, p);
+ if (!WARN_ON_ONCE(dsq->id != SCX_DSQ_LOCAL))
+ dispatch_to_local_dsq(rq, dsq, p, p->scx.ddsp_enq_flags);
}
}

--
2.46.0