block/io_uring: convert to blk_io_plug_call() API

Stop using the .bdrv_co_io_plug() API because it is not multi-queue
block layer friendly. Use the new blk_io_plug_call() API to batch I/O
submission instead.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 20230530180959.1108766-5-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/file-posix.c

@@ -2558,11 +2558,6 @@ static void coroutine_fn raw_co_io_plug(BlockDriverState *bs)
         laio_io_plug();
     }
 #endif
-#ifdef CONFIG_LINUX_IO_URING
-    if (s->use_linux_io_uring) {
-        luring_io_plug();
-    }
-#endif
 }
 
 static void coroutine_fn raw_co_io_unplug(BlockDriverState *bs)
@@ -2573,11 +2568,6 @@ static void coroutine_fn raw_co_io_unplug(BlockDriverState *bs)
         laio_io_unplug(s->aio_max_batch);
     }
 #endif
-#ifdef CONFIG_LINUX_IO_URING
-    if (s->use_linux_io_uring) {
-        luring_io_unplug();
-    }
-#endif
 }
 
 static int coroutine_fn raw_co_flush_to_disk(BlockDriverState *bs)

block/io_uring.c

@@ -16,6 +16,7 @@
 #include "block/raw-aio.h"
 #include "qemu/coroutine.h"
 #include "qapi/error.h"
+#include "sysemu/block-backend.h"
 #include "trace.h"
 
 /* Only used for assertions.  */
@@ -41,7 +42,6 @@ typedef struct LuringAIOCB {
 } LuringAIOCB;
 
 typedef struct LuringQueue {
-    int plugged;
     unsigned int in_queue;
     unsigned int in_flight;
     bool blocked;
@@ -267,7 +267,7 @@ static void luring_process_completions_and_submit(LuringState *s)
 {
     luring_process_completions(s);
 
-    if (!s->io_q.plugged && s->io_q.in_queue > 0) {
+    if (s->io_q.in_queue > 0) {
         ioq_submit(s);
     }
 }
@@ -301,29 +301,17 @@ static void qemu_luring_poll_ready(void *opaque)
 static void ioq_init(LuringQueue *io_q)
 {
     QSIMPLEQ_INIT(&io_q->submit_queue);
-    io_q->plugged = 0;
     io_q->in_queue = 0;
     io_q->in_flight = 0;
     io_q->blocked = false;
 }
 
-void luring_io_plug(void)
+static void luring_unplug_fn(void *opaque)
 {
-    AioContext *ctx = qemu_get_current_aio_context();
-    LuringState *s = aio_get_linux_io_uring(ctx);
-    trace_luring_io_plug(s);
-    s->io_q.plugged++;
-}
-
-void luring_io_unplug(void)
-{
-    AioContext *ctx = qemu_get_current_aio_context();
-    LuringState *s = aio_get_linux_io_uring(ctx);
-    assert(s->io_q.plugged);
-    trace_luring_io_unplug(s, s->io_q.blocked, s->io_q.plugged,
-                           s->io_q.in_queue, s->io_q.in_flight);
-    if (--s->io_q.plugged == 0 &&
-        !s->io_q.blocked && s->io_q.in_queue > 0) {
+    LuringState *s = opaque;
+    trace_luring_unplug_fn(s, s->io_q.blocked, s->io_q.in_queue,
+                           s->io_q.in_flight);
+    if (!s->io_q.blocked && s->io_q.in_queue > 0) {
         ioq_submit(s);
     }
 }
@@ -370,14 +358,16 @@ static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
 
     QSIMPLEQ_INSERT_TAIL(&s->io_q.submit_queue, luringcb, next);
     s->io_q.in_queue++;
-    trace_luring_do_submit(s, s->io_q.blocked, s->io_q.plugged,
-                           s->io_q.in_queue, s->io_q.in_flight);
-    if (!s->io_q.blocked &&
-        (!s->io_q.plugged ||
-         s->io_q.in_flight + s->io_q.in_queue >= MAX_ENTRIES)) {
-        ret = ioq_submit(s);
-        trace_luring_do_submit_done(s, ret);
-        return ret;
+    trace_luring_do_submit(s, s->io_q.blocked, s->io_q.in_queue,
+                           s->io_q.in_flight);
+    if (!s->io_q.blocked) {
+        if (s->io_q.in_flight + s->io_q.in_queue >= MAX_ENTRIES) {
+            ret = ioq_submit(s);
+            trace_luring_do_submit_done(s, ret);
+            return ret;
+        }
+
+        blk_io_plug_call(luring_unplug_fn, s);
     }
     return 0;
 }

block/trace-events

@@ -64,9 +64,8 @@ file_paio_submit(void *acb, void *opaque, int64_t offset, int count, int type) "
 # io_uring.c
 luring_init_state(void *s, size_t size) "s %p size %zu"
 luring_cleanup_state(void *s) "%p freed"
-luring_io_plug(void *s) "LuringState %p plug"
-luring_io_unplug(void *s, int blocked, int plugged, int queued, int inflight) "LuringState %p blocked %d plugged %d queued %d inflight %d"
-luring_do_submit(void *s, int blocked, int plugged, int queued, int inflight) "LuringState %p blocked %d plugged %d queued %d inflight %d"
+luring_unplug_fn(void *s, int blocked, int queued, int inflight) "LuringState %p blocked %d queued %d inflight %d"
+luring_do_submit(void *s, int blocked, int queued, int inflight) "LuringState %p blocked %d queued %d inflight %d"
 luring_do_submit_done(void *s, int ret) "LuringState %p submitted to kernel %d"
 luring_co_submit(void *bs, void *s, void *luringcb, int fd, uint64_t offset, size_t nbytes, int type) "bs %p s %p luringcb %p fd %d offset %" PRId64 " nbytes %zd type %d"
 luring_process_completion(void *s, void *aiocb, int ret) "LuringState %p luringcb %p ret %d"

include/block/raw-aio.h

@@ -81,13 +81,6 @@ int coroutine_fn luring_co_submit(BlockDriverState *bs, int fd, uint64_t offset,
                                   QEMUIOVector *qiov, int type);
 void luring_detach_aio_context(LuringState *s, AioContext *old_context);
 void luring_attach_aio_context(LuringState *s, AioContext *new_context);
-
-/*
- * luring_io_plug/unplug work in the thread's current AioContext, therefore the
- * caller must ensure that they are paired in the same IOThread.
- */
-void luring_io_plug(void);
-void luring_io_unplug(void);
 #endif
 
 #ifdef _WIN32