[PATCH v4 5/5] block/block-copy: use aio-task-pool API

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

Run block_copy iterations in parallel in aio tasks.

Changes:
  - BlockCopyTask becomes aio task structure. Add zeroes field to pass
    it to block_copy_do_copy
  - add call state - it's a state of one call of block_copy(), shared
    between parallel tasks. For now used only to keep information about
    first error: is it read or not.
  - convert block_copy_dirty_clusters to aio-task loop.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/block-copy.c | 119 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 106 insertions(+), 13 deletions(-)

diff --git a/block/block-copy.c b/block/block-copy.c
index f560338647..03500680f7 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -19,15 +19,29 @@
 #include "block/block-copy.h"
 #include "sysemu/block-backend.h"
 #include "qemu/units.h"
+#include "qemu/coroutine.h"
+#include "block/aio_task.h"
 
 #define BLOCK_COPY_MAX_COPY_RANGE (16 * MiB)
 #define BLOCK_COPY_MAX_BUFFER (1 * MiB)
 #define BLOCK_COPY_MAX_MEM (128 * MiB)
+#define BLOCK_COPY_MAX_WORKERS 64
+
+static coroutine_fn int block_copy_task_entry(AioTask *task);
+
+typedef struct BlockCopyCallState {
+    bool failed;
+    bool error_is_read;
+} BlockCopyCallState;
 
 typedef struct BlockCopyTask {
+    AioTask task;
+
     BlockCopyState *s;
+    BlockCopyCallState *call_state;
     int64_t offset;
     int64_t bytes;
+    bool zeroes;
     QLIST_ENTRY(BlockCopyTask) list;
     CoQueue wait_queue; /* coroutines blocked on this task */
 } BlockCopyTask;
@@ -116,6 +130,7 @@ static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t offset,
  * the beginning of it.
  */
 static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
+                                             BlockCopyCallState *call_state,
                                              int64_t offset, int64_t bytes)
 {
     BlockCopyTask *task;
@@ -135,7 +150,9 @@ static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
 
     task = g_new(BlockCopyTask, 1);
     *task = (BlockCopyTask) {
+        .task.func = block_copy_task_entry,
         .s = s,
+        .call_state = call_state,
         .offset = offset,
         .bytes = bytes,
     };
@@ -263,6 +280,38 @@ void block_copy_set_progress_meter(BlockCopyState *s, ProgressMeter *pm)
     s->progress = pm;
 }
 
+/*
+ * Takes ownership of @task
+ *
+ * If pool is NULL directly run the task, otherwise schedule it into the pool.
+ *
+ * Returns: task.func return code if pool is NULL
+ *          otherwise -ECANCELED if pool status is bad
+ *          otherwise 0 (successfully scheduled)
+ */
+static coroutine_fn int block_copy_task_run(AioTaskPool *pool,
+                                            BlockCopyTask *task)
+{
+    if (!pool) {
+        int ret = task->task.func(&task->task);
+
+        g_free(task);
+        return ret;
+    }
+
+    aio_task_pool_wait_slot(pool);
+    if (aio_task_pool_status(pool) < 0) {
+        co_put_to_shres(task->s->mem, task->bytes);
+        block_copy_task_end(task, -ECANCELED);
+        g_free(task);
+        return -ECANCELED;
+    }
+
+    aio_task_pool_start_task(pool, &task->task);
+
+    return 0;
+}
+
 /*
  * block_copy_do_copy
  *
@@ -366,6 +415,27 @@ out:
     return ret;
 }
 
+static coroutine_fn int block_copy_task_entry(AioTask *task)
+{
+    BlockCopyTask *t = container_of(task, BlockCopyTask, task);
+    bool error_is_read;
+    int ret;
+
+    ret = block_copy_do_copy(t->s, t->offset, t->bytes, t->zeroes,
+                             &error_is_read);
+    if (ret < 0 && !t->call_state->failed) {
+        t->call_state->failed = true;
+        t->call_state->error_is_read = error_is_read;
+    } else {
+        progress_work_done(t->s->progress, t->bytes);
+        t->s->progress_bytes_callback(t->bytes, t->s->progress_opaque);
+    }
+    co_put_to_shres(t->s->mem, t->bytes);
+    block_copy_task_end(t, ret);
+
+    return ret;
+}
+
 static int block_copy_block_status(BlockCopyState *s, int64_t offset,
                                    int64_t bytes, int64_t *pnum)
 {
@@ -484,6 +554,8 @@ static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
     int ret = 0;
     bool found_dirty = false;
     int64_t end = offset + bytes;
+    AioTaskPool *aio = NULL;
+    BlockCopyCallState call_state = {false, false};
 
     /*
      * block_copy() user is responsible for keeping source and target in same
@@ -495,11 +567,11 @@ static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
     assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
     assert(QEMU_IS_ALIGNED(bytes, s->cluster_size));
 
-    while (bytes) {
-        g_autofree BlockCopyTask *task = NULL;
+    while (bytes && aio_task_pool_status(aio) == 0) {
+        BlockCopyTask *task;
         int64_t status_bytes;
 
-        task = block_copy_task_create(s, offset, bytes);
+        task = block_copy_task_create(s, &call_state, offset, bytes);
         if (!task) {
             /* No more dirty bits in the bitmap */
             trace_block_copy_skip_range(s, offset, bytes);
@@ -519,6 +591,7 @@ static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
         }
         if (s->skip_unallocated && !(ret & BDRV_BLOCK_ALLOCATED)) {
             block_copy_task_end(task, 0);
+            g_free(task);
             progress_set_remaining(s->progress,
                                    bdrv_get_dirty_count(s->copy_bitmap) +
                                    s->in_flight_bytes);
@@ -527,25 +600,45 @@ static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
             bytes = end - offset;
             continue;
         }
+        task->zeroes = ret & BDRV_BLOCK_ZERO;
 
         trace_block_copy_process(s, task->offset);
 
         co_get_from_shres(s->mem, task->bytes);
-        ret = block_copy_do_copy(s, task->offset, task->bytes,
-                                 ret & BDRV_BLOCK_ZERO, error_is_read);
-        co_put_to_shres(s->mem, task->bytes);
-        block_copy_task_end(task, ret);
-        if (ret < 0) {
-            return ret;
-        }
 
-        progress_work_done(s->progress, task->bytes);
-        s->progress_bytes_callback(task->bytes, s->progress_opaque);
         offset = task_end(task);
         bytes = end - offset;
+
+        if (!aio && bytes) {
+            aio = aio_task_pool_new(BLOCK_COPY_MAX_WORKERS);
+        }
+
+        ret = block_copy_task_run(aio, task);
+        if (ret < 0) {
+            goto out;
+        }
+    }
+
+out:
+    if (aio) {
+        aio_task_pool_wait_all(aio);
+
+        /*
+         * We are not really interested in -ECANCELED returned from
+         * block_copy_task_run. If it fails, it means some task already failed
+         * for real reason, let's return first failure.
+         * Still, assert that we don't rewrite failure by success.
+         */
+        assert(ret == 0 || aio_task_pool_status(aio) < 0);
+        ret = aio_task_pool_status(aio);
+
+        aio_task_pool_free(aio);
+    }
+    if (error_is_read && ret < 0) {
+        *error_is_read = call_state.error_is_read;
     }
 
-    return found_dirty;
+    return ret < 0 ? ret : found_dirty;
 }
 
 /*
-- 
2.21.0