[PATCH v3 2/6] ANDROID: binder: add min sched_policy to node.

[Martijn Coenen]

This change adds flags to flat_binder_object.flags
to allow indicating a minimum scheduling policy for
the node. It also clarifies the valid value range
for the priority bits in the flags.

Internally, we use the priority map that the kernel
uses, e.g. [0..99] for real-time policies and [100..139]
for the SCHED_NORMAL/SCHED_BATCH policies.

Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
---
 drivers/android/binder.c            | 28 +++++++++++++++++--------
 include/uapi/linux/android/binder.h | 41 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 60 insertions(+), 9 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index be6e7e753013..5d51a17dba12 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -352,6 +352,8 @@ struct binder_error {
  *                        and by @lock)
  * @has_async_transaction: async transaction to node in progress
  *                        (protected by @lock)
+ * @sched_policy:         minimum scheduling policy for node
+ *                        (invariant after initialized)
  * @accept_fds:           file descriptor operations supported for node
  *                        (invariant after initialized)
  * @min_priority:         minimum scheduling priority
@@ -391,6 +393,7 @@ struct binder_node {
 		/*
 		 * invariant after initialization
 		 */
+		u8 sched_policy:2;
 		u8 accept_fds:1;
 		u8 min_priority;
 	};
@@ -1256,6 +1259,7 @@ static struct binder_node *binder_init_node_ilocked(
 	binder_uintptr_t ptr = fp ? fp->binder : 0;
 	binder_uintptr_t cookie = fp ? fp->cookie : 0;
 	__u32 flags = fp ? fp->flags : 0;
+	s8 priority;
 
 	assert_spin_locked(&proc->inner_lock);
 
@@ -1288,8 +1292,10 @@ static struct binder_node *binder_init_node_ilocked(
 	node->ptr = ptr;
 	node->cookie = cookie;
 	node->work.type = BINDER_WORK_NODE;
-	node->min_priority = NICE_TO_PRIO(
-			flags & FLAT_BINDER_FLAG_PRIORITY_MASK);
+	priority = flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
+	node->sched_policy = (flags & FLAT_BINDER_FLAG_SCHED_POLICY_MASK) >>
+		FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT;
+	node->min_priority = to_kernel_prio(node->sched_policy, priority);
 	node->accept_fds = !!(flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
 	spin_lock_init(&node->lock);
 	INIT_LIST_HEAD(&node->work.entry);
@@ -4125,12 +4131,17 @@ static int binder_thread_read(struct binder_proc *proc,
 			tr.cookie =  target_node->cookie;
 			t->saved_priority.sched_policy = current->policy;
 			t->saved_priority.prio = current->normal_prio;
-			if (target_node->min_priority < t->priority.prio) {
-				/* The min_priority on a node can currently
-				 * only use SCHED_NORMAL, so we can just
-				 * hardcode this here.
+			if (target_node->min_priority < t->priority.prio ||
+			    (target_node->min_priority == t->priority.prio &&
+			     target_node->sched_policy == SCHED_FIFO)) {
+				/*
+				 * In case the minimum priority on the node is
+				 * higher (lower value), use that priority. If
+				 * the priority is the same, but the node uses
+				 * SCHED_FIFO, prefer SCHED_FIFO, since it can
+				 * run unbounded, unlike SCHED_RR.
 				 */
-				prio.sched_policy = SCHED_NORMAL;
+				prio.sched_policy = target_node->sched_policy;
 				prio.prio = target_node->min_priority;
 			}
 			binder_set_priority(current, prio);
@@ -5205,8 +5216,9 @@ static void print_binder_node_nilocked(struct seq_file *m,
 	hlist_for_each_entry(ref, &node->refs, node_entry)
 		count++;
 
-	seq_printf(m, "  node %d: u%016llx c%016llx hs %d hw %d ls %d lw %d is %d iw %d tr %d",
+	seq_printf(m, "  node %d: u%016llx c%016llx pri %d:%d hs %d hw %d ls %d lw %d is %d iw %d tr %d",
 		   node->debug_id, (u64)node->ptr, (u64)node->cookie,
+		   node->sched_policy, node->min_priority,
 		   node->has_strong_ref, node->has_weak_ref,
 		   node->local_strong_refs, node->local_weak_refs,
 		   node->internal_strong_refs, count, node->tmp_refs);
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index 84a9a0944e13..b3bced80adea 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -37,9 +37,48 @@ enum {
 	BINDER_TYPE_PTR		= B_PACK_CHARS('p', 't', '*', B_TYPE_LARGE),
 };
 
-enum {
+/**
+ * enum flat_binder_object_shifts: shift values for flat_binder_object_flags
+ * @FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT: shift for getting scheduler policy.
+ *
+ */
+enum flat_binder_object_shifts {
+	FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT = 9,
+};
+
+/**
+ * enum flat_binder_object_flags - flags for use in flat_binder_object.flags
+ */
+enum flat_binder_object_flags {
+	/**
+	 * @FLAT_BINDER_FLAG_PRIORITY_MASK: bit-mask for min scheduler priority
+	 *
+	 * These bits can be used to set the minimum scheduler priority
+	 * at which transactions into this node should run. Valid values
+	 * in these bits depend on the scheduler policy encoded in
+	 * @FLAT_BINDER_FLAG_SCHED_POLICY_MASK.
+	 *
+	 * For SCHED_NORMAL/SCHED_BATCH, the valid range is between [-20..19]
+	 * For SCHED_FIFO/SCHED_RR, the value can run between [1..99]
+	 */
 	FLAT_BINDER_FLAG_PRIORITY_MASK = 0xff,
+	/**
+	 * @FLAT_BINDER_FLAG_ACCEPTS_FDS: whether the node accepts fds.
+	 */
 	FLAT_BINDER_FLAG_ACCEPTS_FDS = 0x100,
+	/**
+	 * @FLAT_BINDER_FLAG_SCHED_POLICY_MASK: bit-mask for scheduling policy
+	 *
+	 * These two bits can be used to set the min scheduling policy at which
+	 * transactions on this node should run. These match the UAPI
+	 * scheduler policy values, eg:
+	 * 00b: SCHED_NORMAL
+	 * 01b: SCHED_FIFO
+	 * 10b: SCHED_RR
+	 * 11b: SCHED_BATCH
+	 */
+	FLAT_BINDER_FLAG_SCHED_POLICY_MASK =
+		3U << FLAT_BINDER_FLAG_SCHED_POLICY_SHIFT,
 };
 
 #ifdef BINDER_IPC_32BIT
-- 
2.15.0.rc2.357.g7e34df9404-goog