ANDROID: binder: Add thread->process_todo flag.

This flag determines whether the thread should currently
process the work in the thread->todo worklist.

The prime usecase for this is improving the performance
of synchronous transactions: all synchronous transactions
post a BR_TRANSACTION_COMPLETE to the calling thread,
but there's no reason to return that command to userspace
right away - userspace anyway needs to wait for the reply.

Likewise, a synchronous transaction that contains a binder
object can cause a BC_ACQUIRE/BC_INCREFS to be returned to
userspace; since the caller must anyway hold a strong/weak
ref for the duration of the call, postponing these commands
until the reply comes in is not a problem.

Note that this flag is not used to determine whether a
thread can handle process work; a thread should never pick
up process work when thread work is still pending.

Before patch:
------------------------------------------------------------------
Benchmark                           Time           CPU Iterations
------------------------------------------------------------------
BM_sendVec_binderize/4          45959 ns      20288 ns      34351
BM_sendVec_binderize/8          45603 ns      20080 ns      34909
BM_sendVec_binderize/16         45528 ns      20113 ns      34863
BM_sendVec_binderize/32         45551 ns      20122 ns      34881
BM_sendVec_binderize/64         45701 ns      20183 ns      34864
BM_sendVec_binderize/128        45824 ns      20250 ns      34576
BM_sendVec_binderize/256        45695 ns      20171 ns      34759
BM_sendVec_binderize/512        45743 ns      20211 ns      34489
BM_sendVec_binderize/1024       46169 ns      20430 ns      34081

After patch:
------------------------------------------------------------------
Benchmark                           Time           CPU Iterations
------------------------------------------------------------------
BM_sendVec_binderize/4          42939 ns      17262 ns      40653
BM_sendVec_binderize/8          42823 ns      17243 ns      40671
BM_sendVec_binderize/16         42898 ns      17243 ns      40594
BM_sendVec_binderize/32         42838 ns      17267 ns      40527
BM_sendVec_binderize/64         42854 ns      17249 ns      40379
BM_sendVec_binderize/128        42881 ns      17288 ns      40427
BM_sendVec_binderize/256        42917 ns      17297 ns      40429
BM_sendVec_binderize/512        43184 ns      17395 ns      40411
BM_sendVec_binderize/1024       43119 ns      17357 ns      40432

Signed-off-by: Martijn Coenen <maco@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index a73596a4f804c817bfd277d3ff51eb42ca969bae..e9d22dd85a19fd58ffe7eeac9c512d5faeb5b52b 100644 (file)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -577,6 +577,8 @@ enum {
  *                        (protected by @proc->inner_lock)
  * @todo:                 list of work to do for this thread
  *                        (protected by @proc->inner_lock)
+ * @process_todo:         whether work in @todo should be processed
+ *                        (protected by @proc->inner_lock)
  * @return_error:         transaction errors reported by this thread
  *                        (only accessed by this thread)
  * @reply_error:          transaction errors reported by target thread
@@ -602,6 +604,7 @@ struct binder_thread {
        bool looper_need_return; /* can be written by other thread */
        struct binder_transaction *transaction_stack;
        struct list_head todo;
+       bool process_todo;
        struct binder_error return_error;
        struct binder_error reply_error;
        wait_queue_head_t wait;
@@ -787,6 +790,16 @@ static bool binder_worklist_empty(struct binder_proc *proc,
        return ret;
 }
 
+/**
+ * binder_enqueue_work_ilocked() - Add an item to the work list
+ * @work:         struct binder_work to add to list
+ * @target_list:  list to add work to
+ *
+ * Adds the work to the specified list. Asserts that work
+ * is not already on a list.
+ *
+ * Requires the proc->inner_lock to be held.
+ */
 static void
 binder_enqueue_work_ilocked(struct binder_work *work,
                           struct list_head *target_list)
@@ -797,22 +810,56 @@ binder_enqueue_work_ilocked(struct binder_work *work,
 }
 
 /**
- * binder_enqueue_work() - Add an item to the work list
- * @proc:         binder_proc associated with list
+ * binder_enqueue_deferred_thread_work_ilocked() - Add deferred thread work
+ * @thread:       thread to queue work to
  * @work:         struct binder_work to add to list
- * @target_list:  list to add work to
  *
- * Adds the work to the specified list. Asserts that work
- * is not already on a list.
+ * Adds the work to the todo list of the thread. Doesn't set the process_todo
+ * flag, which means that (if it wasn't already set) the thread will go to
+ * sleep without handling this work when it calls read.
+ *
+ * Requires the proc->inner_lock to be held.
  */
 static void
-binder_enqueue_work(struct binder_proc *proc,
-                   struct binder_work *work,
-                   struct list_head *target_list)
+binder_enqueue_deferred_thread_work_ilocked(struct binder_thread *thread,
+                                           struct binder_work *work)
 {
-       binder_inner_proc_lock(proc);
-       binder_enqueue_work_ilocked(work, target_list);
-       binder_inner_proc_unlock(proc);
+       binder_enqueue_work_ilocked(work, &thread->todo);
+}
+
+/**
+ * binder_enqueue_thread_work_ilocked() - Add an item to the thread work list
+ * @thread:       thread to queue work to
+ * @work:         struct binder_work to add to list
+ *
+ * Adds the work to the todo list of the thread, and enables processing
+ * of the todo queue.
+ *
+ * Requires the proc->inner_lock to be held.
+ */
+static void
+binder_enqueue_thread_work_ilocked(struct binder_thread *thread,
+                                  struct binder_work *work)
+{
+       binder_enqueue_work_ilocked(work, &thread->todo);
+       thread->process_todo = true;
+}
+
+/**
+ * binder_enqueue_thread_work() - Add an item to the thread work list
+ * @thread:       thread to queue work to
+ * @work:         struct binder_work to add to list
+ *
+ * Adds the work to the todo list of the thread, and enables processing
+ * of the todo queue.
+ */
+static void
+binder_enqueue_thread_work(struct binder_thread *thread,
+                          struct binder_work *work)
+{
+       binder_inner_proc_lock(thread->proc);
+       binder_enqueue_thread_work_ilocked(thread, work);
+       binder_inner_proc_unlock(thread->proc);
 }
 
 static void
@@ -927,7 +974,7 @@ static long task_close_fd(struct binder_proc *proc, unsigned int fd)
 static bool binder_has_work_ilocked(struct binder_thread *thread,
                                    bool do_proc_work)
 {
-       return !binder_worklist_empty_ilocked(&thread->todo) ||
+       return thread->process_todo ||
                thread->looper_need_return ||
                (do_proc_work &&
                 !binder_worklist_empty_ilocked(&thread->proc->todo));
@@ -1215,6 +1262,17 @@ static int binder_inc_node_nilocked(struct binder_node *node, int strong,
                        node->local_strong_refs++;
                if (!node->has_strong_ref && target_list) {
                        binder_dequeue_work_ilocked(&node->work);
+                       /*
+                        * Note: this function is the only place where we queue
+                        * directly to a thread->todo without using the
+                        * corresponding binder_enqueue_thread_work() helper
+                        * functions; in this case it's ok to not set the
+                        * process_todo flag, since we know this node work will
+                        * always be followed by other work that starts queue
+                        * processing: in case of synchronous transactions, a
+                        * BR_REPLY or BR_ERROR; in case of oneway
+                        * transactions, a BR_TRANSACTION_COMPLETE.
+                        */
                        binder_enqueue_work_ilocked(&node->work, target_list);
                }
        } else {
@@ -1226,6 +1284,9 @@ static int binder_inc_node_nilocked(struct binder_node *node, int strong,
                                        node->debug_id);
                                return -EINVAL;
                        }
+                       /*
+                        * See comment above
+                        */
                        binder_enqueue_work_ilocked(&node->work, target_list);
                }
        }
@@ -1915,9 +1976,9 @@ static void binder_send_failed_reply(struct binder_transaction *t,
                        binder_pop_transaction_ilocked(target_thread, t);
                        if (target_thread->reply_error.cmd == BR_OK) {
                                target_thread->reply_error.cmd = error_code;
-                               binder_enqueue_work_ilocked(
-                                       &target_thread->reply_error.work,
-                                       &target_thread->todo);
+                               binder_enqueue_thread_work_ilocked(
+                                       target_thread,
+                                       &target_thread->reply_error.work);
                                wake_up_interruptible(&target_thread->wait);
                        } else {
                                WARN(1, "Unexpected reply error: %u\n",
@@ -2536,18 +2597,16 @@ static bool binder_proc_transaction(struct binder_transaction *t,
                                    struct binder_proc *proc,
                                    struct binder_thread *thread)
 {
-       struct list_head *target_list = NULL;
        struct binder_node *node = t->buffer->target_node;
        bool oneway = !!(t->flags & TF_ONE_WAY);
-       bool wakeup = true;
+       bool pending_async = false;
 
        BUG_ON(!node);
        binder_node_lock(node);
        if (oneway) {
                BUG_ON(thread);
                if (node->has_async_transaction) {
-                       target_list = &node->async_todo;
-                       wakeup = false;
+                       pending_async = true;
                } else {
                        node->has_async_transaction = 1;
                }
@@ -2561,19 +2620,17 @@ static bool binder_proc_transaction(struct binder_transaction *t,
                return false;
        }
 
-       if (!thread && !target_list)
+       if (!thread && !pending_async)
                thread = binder_select_thread_ilocked(proc);
 
        if (thread)
-               target_list = &thread->todo;
-       else if (!target_list)
-               target_list = &proc->todo;
+               binder_enqueue_thread_work_ilocked(thread, &t->work);
+       else if (!pending_async)
+               binder_enqueue_work_ilocked(&t->work, &proc->todo);
        else
-               BUG_ON(target_list != &node->async_todo);
-
-       binder_enqueue_work_ilocked(&t->work, target_list);
+               binder_enqueue_work_ilocked(&t->work, &node->async_todo);
 
-       if (wakeup)
+       if (!pending_async)
                binder_wakeup_thread_ilocked(proc, thread, !oneway /* sync */);
 
        binder_inner_proc_unlock(proc);
@@ -3068,10 +3125,10 @@ static void binder_transaction(struct binder_proc *proc,
                }
        }
        tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
-       binder_enqueue_work(proc, tcomplete, &thread->todo);
        t->work.type = BINDER_WORK_TRANSACTION;
 
        if (reply) {
+               binder_enqueue_thread_work(thread, tcomplete);
                binder_inner_proc_lock(target_proc);
                if (target_thread->is_dead) {
                        binder_inner_proc_unlock(target_proc);
@@ -3079,13 +3136,21 @@ static void binder_transaction(struct binder_proc *proc,
                }
                BUG_ON(t->buffer->async_transaction != 0);
                binder_pop_transaction_ilocked(target_thread, in_reply_to);
-               binder_enqueue_work_ilocked(&t->work, &target_thread->todo);
+               binder_enqueue_thread_work_ilocked(target_thread, &t->work);
                binder_inner_proc_unlock(target_proc);
                wake_up_interruptible_sync(&target_thread->wait);
                binder_free_transaction(in_reply_to);
        } else if (!(t->flags & TF_ONE_WAY)) {
                BUG_ON(t->buffer->async_transaction != 0);
                binder_inner_proc_lock(proc);
+               /*
+                * Defer the TRANSACTION_COMPLETE, so we don't return to
+                * userspace immediately; this allows the target process to
+                * immediately start processing this transaction, reducing
+                * latency. We will then return the TRANSACTION_COMPLETE when
+                * the target replies (or there is an error).
+                */
+               binder_enqueue_deferred_thread_work_ilocked(thread, tcomplete);
                t->need_reply = 1;
                t->from_parent = thread->transaction_stack;
                thread->transaction_stack = t;
@@ -3099,6 +3164,7 @@ static void binder_transaction(struct binder_proc *proc,
        } else {
                BUG_ON(target_node == NULL);
                BUG_ON(t->buffer->async_transaction != 1);
+               binder_enqueue_thread_work(thread, tcomplete);
                if (!binder_proc_transaction(t, target_proc, NULL))
                        goto err_dead_proc_or_thread;
        }
@@ -3177,15 +3243,11 @@ err_invalid_target_handle:
        BUG_ON(thread->return_error.cmd != BR_OK);
        if (in_reply_to) {
                thread->return_error.cmd = BR_TRANSACTION_COMPLETE;
-               binder_enqueue_work(thread->proc,
-                                   &thread->return_error.work,
-                                   &thread->todo);
+               binder_enqueue_thread_work(thread, &thread->return_error.work);
                binder_send_failed_reply(in_reply_to, return_error);
        } else {
                thread->return_error.cmd = return_error;
-               binder_enqueue_work(thread->proc,
-                                   &thread->return_error.work,
-                                   &thread->todo);
+               binder_enqueue_thread_work(thread, &thread->return_error.work);
        }
 }
 
@@ -3489,10 +3551,9 @@ static int binder_thread_write(struct binder_proc *proc,
                                        WARN_ON(thread->return_error.cmd !=
                                                BR_OK);
                                        thread->return_error.cmd = BR_ERROR;
-                                       binder_enqueue_work(
-                                               thread->proc,
-                                               &thread->return_error.work,
-                                               &thread->todo);
+                                       binder_enqueue_thread_work(
+                                               thread,
+                                               &thread->return_error.work);
                                        binder_debug(
                                                BINDER_DEBUG_FAILED_TRANSACTION,
                                                "%d:%d BC_REQUEST_DEATH_NOTIFICATION failed\n",
@@ -3572,9 +3633,9 @@ static int binder_thread_write(struct binder_proc *proc,
                                        if (thread->looper &
                                            (BINDER_LOOPER_STATE_REGISTERED |
                                             BINDER_LOOPER_STATE_ENTERED))
-                                               binder_enqueue_work_ilocked(
-                                                               &death->work,
-                                                               &thread->todo);
+                                               binder_enqueue_thread_work_ilocked(
+                                                               thread,
+                                                               &death->work);
                                        else {
                                                binder_enqueue_work_ilocked(
                                                                &death->work,
@@ -3629,8 +3690,8 @@ static int binder_thread_write(struct binder_proc *proc,
                                if (thread->looper &
                                        (BINDER_LOOPER_STATE_REGISTERED |
                                         BINDER_LOOPER_STATE_ENTERED))
-                                       binder_enqueue_work_ilocked(
-                                               &death->work, &thread->todo);
+                                       binder_enqueue_thread_work_ilocked(
+                                               thread, &death->work);
                                else {
                                        binder_enqueue_work_ilocked(
                                                        &death->work,
@@ -3804,6 +3865,8 @@ retry:
                        break;
                }
                w = binder_dequeue_work_head_ilocked(list);
+               if (binder_worklist_empty_ilocked(&thread->todo))
+                       thread->process_todo = false;
 
                switch (w->type) {
                case BINDER_WORK_TRANSACTION: {