[Qemu-devel] [PATCH v4 0/9] Add support for io_uring

[Qemu-devel] [PATCH v4 0/9] Add support for io_uring

[Aarushi Mehta]

This patch series adds support for the newly developed io_uring Linux AIO
interface. Linux io_uring is faster than Linux's AIO asynchronous I/O code,
offers efficient buffered asynchronous I/O support, the ability to do I/O
without performing a system call via polled I/O, and other efficiency enhancements.

Testing it requires a host kernel (5.1+) and the liburing library.
Use the option -drive aio=io_uring to enable it.

v4:
- Add error handling
- Add trace events
- Remove aio submission based code

v3:
- Fix major errors in io_uring (sorry)
- Option now enumerates for CONFIG_LINUX_IO_URING
- pkg config support added

Aarushi Mehta (9):
  configure: permit use of io_uring
  qapi/block-core: add option for io_uring
  block/block: add BDRV flag for io_uring
  block/io_uring: implements interfaces for io_uring
  stubs: add stubs for io_uring interface
  util/async: add aio interfaces for io_uring
  blockdev: accept io_uring as option
  block/file-posix.c: extend to use io_uring
  block: add trace events for io_uring

 MAINTAINERS             |   8 +
 block/Makefile.objs     |   3 +
 block/file-posix.c      |  85 +++++++++--
 block/io_uring.c        | 325 ++++++++++++++++++++++++++++++++++++++++
 block/trace-events      |   8 +
 blockdev.c              |   4 +-
 configure               |  27 ++++
 include/block/aio.h     |  16 +-
 include/block/block.h   |   1 +
 include/block/raw-aio.h |  12 ++
 qapi/block-core.json    |   4 +-
 stubs/Makefile.objs     |   1 +
 stubs/io_uring.c        |  32 ++++
 util/async.c            |  36 +++++
 14 files changed, 543 insertions(+), 19 deletions(-)
 create mode 100644 block/io_uring.c
 create mode 100644 stubs/io_uring.c

-- 
2.17.1

[Qemu-devel] [PATCH v4 1/9] configure: permit use of io_uring

[Aarushi Mehta]

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 configure | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/configure b/configure
index 6cdcfb2dc3..cb49ef0fcc 100755
--- a/configure
+++ b/configure
@@ -365,6 +365,7 @@ xen=""
 xen_ctrl_version=""
 xen_pci_passthrough=""
 linux_aio=""
+linux_io_uring=""
 cap_ng=""
 attr=""
 libattr=""
@@ -1266,6 +1267,10 @@ for opt do
   ;;
   --enable-linux-aio) linux_aio="yes"
   ;;
+  --disable-linux-io-uring) linux_io_uring="no"
+  ;;
+  --enable-linux-io-uring) linux_io_uring="yes"
+  ;;
   --disable-attr) attr="no"
   ;;
   --enable-attr) attr="yes"
@@ -1784,6 +1789,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   vde             support for vde network
   netmap          support for netmap network
   linux-aio       Linux AIO support
+  linux-io-uring  Linux io_uring support
   cap-ng          libcap-ng support
   attr            attr and xattr support
   vhost-net       vhost-net kernel acceleration support
@@ -3973,6 +3979,21 @@ EOF
     linux_aio=no
   fi
 fi
+##########################################
+# linux-io-uring probe
+
+if test "$linux_io_uring" != "no" ; then
+  if $pkg_config liburing; then
+    linux_io_uring_cflags=$($pkg_config --cflags liburing)
+    linux_io_uring_libs=$($pkg_config --libs liburing)
+    linux_io_uring=yes
+  else
+    if test "$linux_io_uring" = "yes" ; then
+      feature_not_found "linux io_uring" "Install liburing devel"
+    fi
+    linux_io_uring=no
+  fi
+fi
 
 ##########################################
 # TPM emulation is only on POSIX
@@ -6396,6 +6417,7 @@ echo "PIE               $pie"
 echo "vde support       $vde"
 echo "netmap support    $netmap"
 echo "Linux AIO support $linux_aio"
+echo "Linux io_uring support $linux_io_uring"
 echo "ATTR/XATTR support $attr"
 echo "Install blobs     $blobs"
 echo "KVM support       $kvm"
@@ -6876,6 +6898,11 @@ fi
 if test "$linux_aio" = "yes" ; then
   echo "CONFIG_LINUX_AIO=y" >> $config_host_mak
 fi
+if test "$linux_io_uring" = "yes" ; then
+  echo "CONFIG_LINUX_IO_URING=y" >> $config_host_mak
+  echo "LINUX_IO_URING_CFLAGS=$linux_io_uring_cflags" >> $config_host_mak
+  echo "LINUX_IO_URING_LIBS=$linux_io_uring_libs" >> $config_host_mak
+fi
 if test "$attr" = "yes" ; then
   echo "CONFIG_ATTR=y" >> $config_host_mak
 fi
-- 
2.17.1

[Qemu-devel] [PATCH v4 2/9] qapi/block-core: add option for io_uring

[Aarushi Mehta]

Option only enumerates for hosts that support it.
Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 qapi/block-core.json | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1defcde048..db7eedd058 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2792,11 +2792,13 @@
 #
 # @threads:     Use qemu's thread pool
 # @native:      Use native AIO backend (only Linux and Windows)
+# @io_uring:    Use linux io_uring (since 4.1)
 #
 # Since: 2.9
 ##
 { 'enum': 'BlockdevAioOptions',
-  'data': [ 'threads', 'native' ] }
+  'data': [ 'threads', 'native',
+            { 'name': 'io_uring', 'if': 'defined(CONFIG_LINUX_IO_URING)' } ] }
 
 ##
 # @BlockdevCacheOptions:
-- 
2.17.1

[Qemu-devel] [PATCH v4 3/9] block/block: add BDRV flag for io_uring

[Aarushi Mehta]

Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/block/block.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/block/block.h b/include/block/block.h
index 9b083e2bca..60f7c6c01c 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -121,6 +121,7 @@ typedef struct HDGeometry {
                                       ignoring the format layer */
 #define BDRV_O_NO_IO       0x10000 /* don't initialize for I/O */
 #define BDRV_O_AUTO_RDONLY 0x20000 /* degrade to read-only if opening read-write fails */
+#define BDRV_O_IO_URING    0x40000 /* use io_uring instead of the thread pool */
 
 #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_NO_FLUSH)
 
-- 
2.17.1

[Qemu-devel] [PATCH v4 4/9] block/io_uring: implements interfaces for io_uring

[Aarushi Mehta]

Aborts when sqes cannot be set as sqes cannot be returned to ring.
Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 MAINTAINERS             |   7 +
 block/Makefile.objs     |   3 +
 block/io_uring.c        | 315 ++++++++++++++++++++++++++++++++++++++++
 include/block/aio.h     |  16 +-
 include/block/raw-aio.h |  12 ++
 5 files changed, 352 insertions(+), 1 deletion(-)
 create mode 100644 block/io_uring.c

diff --git a/MAINTAINERS b/MAINTAINERS
index a96829ea83..dcaddec21f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2515,6 +2515,13 @@ F: block/file-posix.c
 F: block/file-win32.c
 F: block/win32-aio.c
 
+Linux io_uring
+M: Aarushi Mehta <mehta.aaru20@gmail.com>
+R: Stefan Hajnoczi <stefan@redhat.com>
+L: qemu-block@nongnu.org
+S: Maintained
+F: block/io_uring.c
+
 qcow2
 M: Kevin Wolf <kwolf@redhat.com>
 M: Max Reitz <mreitz@redhat.com>
diff --git a/block/Makefile.objs b/block/Makefile.objs
index ae11605c9f..8fde7a23a5 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -18,6 +18,7 @@ block-obj-y += block-backend.o snapshot.o qapi.o
 block-obj-$(CONFIG_WIN32) += file-win32.o win32-aio.o
 block-obj-$(CONFIG_POSIX) += file-posix.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
+block-obj-$(CONFIG_LINUX_IO_URING) += io_uring.o
 block-obj-y += null.o mirror.o commit.o io.o create.o
 block-obj-y += throttle-groups.o
 block-obj-$(CONFIG_LINUX) += nvme.o
@@ -61,5 +62,7 @@ block-obj-$(if $(CONFIG_LZFSE),m,n) += dmg-lzfse.o
 dmg-lzfse.o-libs   := $(LZFSE_LIBS)
 qcow.o-libs        := -lz
 linux-aio.o-libs   := -laio
+io_uring.o-cflags  := $(LINUX_IO_URING_CFLAGS)
+io_uring.o-libs    := $(LINUX_IO_URING_LIBS)
 parallels.o-cflags := $(LIBXML2_CFLAGS)
 parallels.o-libs   := $(LIBXML2_LIBS)
diff --git a/block/io_uring.c b/block/io_uring.c
new file mode 100644
index 0000000000..536a9fbe87
--- /dev/null
+++ b/block/io_uring.c
@@ -0,0 +1,315 @@
+/*
+ * Linux io_uring support.
+ *
+ * Copyright (C) 2009 IBM, Corp.
+ * Copyright (C) 2009 Red Hat, Inc.
+ * Copyright (C) 2019 Aarushi Mehta
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#include "qemu/osdep.h"
+#include <liburing.h>
+#include "qemu-common.h"
+#include "block/aio.h"
+#include "qemu/queue.h"
+#include "block/block.h"
+#include "block/raw-aio.h"
+#include "qemu/coroutine.h"
+#include "qapi/error.h"
+
+#define MAX_EVENTS 128
+
+typedef struct LuringAIOCB {
+    Coroutine *co;
+    struct io_uring_sqe sqeq;
+    ssize_t ret;
+    QEMUIOVector *qiov;
+    bool is_read;
+    QSIMPLEQ_ENTRY(LuringAIOCB) next;
+} LuringAIOCB;
+
+typedef struct LuringQueue {
+    int plugged;
+    unsigned int in_queue;
+    unsigned int in_flight;
+    bool blocked;
+    QSIMPLEQ_HEAD(, LuringAIOCB) sq_overflow;
+} LuringQueue;
+
+typedef struct LuringState {
+    AioContext *aio_context;
+
+    struct io_uring ring;
+
+    /* io queue for submit at batch.  Protected by AioContext lock. */
+    LuringQueue io_q;
+
+    /* I/O completion processing.  Only runs in I/O thread.  */
+    QEMUBH *completion_bh;
+} LuringState;
+
+/**
+ * ioq_submit:
+ * @s: AIO state
+ *
+ * Queues pending sqes and submits them
+ *
+ */
+static int ioq_submit(LuringState *s);
+
+/**
+ * qemu_luring_process_completions:
+ * @s: AIO state
+ *
+ * Fetches completed I/O requests, consumes cqes and invokes their callbacks.
+ *
+ */
+static void qemu_luring_process_completions(LuringState *s)
+{
+    struct io_uring_cqe *cqes;
+    int ret;
+
+    /*
+     * Request completion callbacks can run the nested event loop.
+     * Schedule ourselves so the nested event loop will "see" remaining
+     * completed requests and process them.  Without this, completion
+     * callbacks that wait for other requests using a nested event loop
+     * would hang forever.
+     */
+    qemu_bh_schedule(s->completion_bh);
+
+    while (io_uring_peek_cqe(&s->ring, &cqes) == 0) {
+        if (!cqes) {
+            break;
+        }
+        LuringAIOCB *luringcb = io_uring_cqe_get_data(cqes);
+        read_barrier();
+        ret = cqes->res;
+
+        if (ret == luringcb->qiov->size) {
+            ret = 0;
+        } else if (ret >= 0) {
+            /* Short Read/Write */
+            if (luringcb->is_read) {
+                /* Read, pad with zeroes */
+                qemu_iovec_memset(luringcb->qiov, ret, 0,
+                luringcb->qiov->size - ret);
+            } else {
+                ret = -ENOSPC;;
+            }
+        }
+        luringcb->ret = ret;
+
+        io_uring_cqe_seen(&s->ring, cqes);
+        cqes = NULL;
+        /* Change counters one-by-one because we can be nested. */
+        s->io_q.in_flight--;
+
+        /*
+         * If the coroutine is already entered it must be in ioq_submit()
+         * and will notice luringcb->ret has been filled in when it
+         * eventually runs later. Coroutines cannot be entered recursively
+         * so avoid doing that!
+         */
+        if (!qemu_coroutine_entered(luringcb->co)) {
+            aio_co_wake(luringcb->co);
+        }
+    }
+    qemu_bh_cancel(s->completion_bh);
+}
+
+static void qemu_luring_process_completions_and_submit(LuringState *s)
+{
+    aio_context_acquire(s->aio_context);
+    qemu_luring_process_completions(s);
+
+    if (!s->io_q.plugged && !s->io_q.in_queue) {
+        ioq_submit(s);
+    }
+    aio_context_release(s->aio_context);
+}
+
+static void qemu_luring_completion_bh(void *opaque)
+{
+    LuringState *s = opaque;
+    qemu_luring_process_completions_and_submit(s);
+}
+
+static void qemu_luring_completion_cb(void *opaque)
+{
+    LuringState *s = opaque;
+    qemu_luring_process_completions_and_submit(s);
+}
+
+static void ioq_init(LuringQueue *io_q)
+{
+    QSIMPLEQ_INIT(&io_q->sq_overflow);
+    io_q->plugged = 0;
+    io_q->in_queue = 0;
+    io_q->in_flight = 0;
+    io_q->blocked = false;
+}
+
+static int ioq_submit(LuringState *s)
+{
+    int ret = 0;
+    LuringAIOCB *luringcb, *luringcb_next;
+
+    while (s->io_q.in_queue > 0) {
+        QSIMPLEQ_FOREACH_SAFE(luringcb, &s->io_q.sq_overflow, next,
+                              luringcb_next) {
+            struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
+            if (!sqes) {
+                break;
+            }
+            /* Prep sqe for submission */
+            *sqes = luringcb->sqeq;
+            QSIMPLEQ_REMOVE_HEAD(&s->io_q.sq_overflow, next);
+        }
+        ret =  io_uring_submit(&s->ring);
+        /* Prevent infinite loop if submission is repeatedly refused */
+        if (ret <= 0) {
+            if (ret == -EAGAIN) {
+                continue;
+            }
+            break;
+        }
+        s->io_q.in_flight += ret;
+        s->io_q.in_queue  -= ret;
+    }
+    s->io_q.blocked = (s->io_q.in_queue > 0);
+
+    if (s->io_q.in_flight) {
+        /*
+         * We can try to complete something just right away if there are
+         * still requests in-flight.
+         */
+        qemu_luring_process_completions(s);
+    }
+    return ret;
+}
+
+void luring_io_plug(BlockDriverState *bs, LuringState *s)
+{
+    s->io_q.plugged++;
+}
+
+void luring_io_unplug(BlockDriverState *bs, LuringState *s)
+{
+    assert(s->io_q.plugged);
+    if (--s->io_q.plugged == 0 &&
+        !s->io_q.blocked && s->io_q.in_queue > 0) {
+        ioq_submit(s);
+    }
+}
+
+/**
+ * luring_do_submit:
+ * @fd: file descriptor for I/O
+ * @luringcb: AIO control block
+ * @s: AIO state
+ * @offset: offset for request
+ * @type: type of request
+ *
+ * Fetches sqes from ring, adds to pending queue and preps them
+ *
+ */
+static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
+                            uint64_t offset, int type)
+{
+    struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
+    if (!sqes) {
+        sqes = &luringcb->sqeq;
+        QSIMPLEQ_INSERT_TAIL(&s->io_q.sq_overflow, luringcb, next);
+    }
+
+    switch (type) {
+    case QEMU_AIO_WRITE:
+        io_uring_prep_writev(sqes, fd, luringcb->qiov->iov,
+                             luringcb->qiov->niov, offset);
+        break;
+    case QEMU_AIO_READ:
+        io_uring_prep_readv(sqes, fd, luringcb->qiov->iov,
+                            luringcb->qiov->niov, offset);
+        break;
+    case QEMU_AIO_FLUSH:
+        io_uring_prep_fsync(sqes, fd, 0);
+        break;
+    default:
+        fprintf(stderr, "%s: invalid AIO request type, aborting 0x%x.\n",
+                        __func__, type);
+        abort();
+    }
+    io_uring_sqe_set_data(sqes, luringcb);
+    s->io_q.in_queue++;
+
+    if (!s->io_q.blocked &&
+        (!s->io_q.plugged ||
+         s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
+        return ioq_submit(s);
+    }
+    return 0;
+}
+
+int coroutine_fn luring_co_submit(BlockDriverState *bs, LuringState *s, int fd,
+                                uint64_t offset, QEMUIOVector *qiov, int type)
+{
+    int ret;
+    LuringAIOCB luringcb = {
+        .co         = qemu_coroutine_self(),
+        .ret        = -EINPROGRESS,
+        .qiov       = qiov,
+        .is_read    = (type == QEMU_AIO_READ),
+    };
+
+    ret = luring_do_submit(fd, &luringcb, s, offset, type);
+    if (ret < 0) {
+        return ret;
+    }
+
+    if (luringcb.ret == -EINPROGRESS) {
+        qemu_coroutine_yield();
+    }
+    return luringcb.ret;
+}
+
+void luring_detach_aio_context(LuringState *s, AioContext *old_context)
+{
+    aio_set_fd_handler(old_context, s->ring.ring_fd, false, NULL, NULL, NULL,
+                       s);
+    qemu_bh_delete(s->completion_bh);
+    s->aio_context = NULL;
+}
+
+void luring_attach_aio_context(LuringState *s, AioContext *new_context)
+{
+    s->aio_context = new_context;
+    s->completion_bh = aio_bh_new(new_context, qemu_luring_completion_bh, s);
+    aio_set_fd_handler(s->aio_context, s->ring.ring_fd, false,
+                       qemu_luring_completion_cb, NULL, NULL, s);
+}
+
+LuringState *luring_init(Error **errp)
+{
+    int rc;
+    LuringState *s;
+    s = g_malloc0(sizeof(*s));
+    struct io_uring *ring = &s->ring;
+    rc =  io_uring_queue_init(MAX_EVENTS, ring, 0);
+    if (rc < 0) {
+        error_setg_errno(errp, errno, "failed to init linux io_uring ring");
+        g_free(s);
+        return NULL;
+    }
+
+    ioq_init(&s->io_q);
+    return s;
+
+}
+
+void luring_cleanup(LuringState *s)
+{
+    io_uring_queue_exit(&s->ring);
+    g_free(s);
+}
diff --git a/include/block/aio.h b/include/block/aio.h
index 0ca25dfec6..9da3fd9793 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -50,6 +50,7 @@ typedef void IOHandler(void *opaque);
 struct Coroutine;
 struct ThreadPool;
 struct LinuxAioState;
+struct LuringState;
 
 struct AioContext {
     GSource source;
@@ -118,11 +119,19 @@ struct AioContext {
     struct ThreadPool *thread_pool;
 
 #ifdef CONFIG_LINUX_AIO
-    /* State for native Linux AIO.  Uses aio_context_acquire/release for
+    /*
+     * State for native Linux AIO.  Uses aio_context_acquire/release for
      * locking.
      */
     struct LinuxAioState *linux_aio;
 #endif
+#ifdef CONFIG_LINUX_IO_URING
+    /*
+     * State for Linux io_uring.  Uses aio_context_acquire/release for
+     * locking.
+     */
+    struct LuringState *linux_io_uring;
+#endif
 
     /* TimerLists for calling timers - one per clock type.  Has its own
      * locking.
@@ -387,6 +396,11 @@ struct LinuxAioState *aio_setup_linux_aio(AioContext *ctx, Error **errp);
 /* Return the LinuxAioState bound to this AioContext */
 struct LinuxAioState *aio_get_linux_aio(AioContext *ctx);
 
+/* Setup the LuringState bound to this AioContext */
+struct LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp);
+
+/* Return the LuringState bound to this AioContext */
+struct LuringState *aio_get_linux_io_uring(AioContext *ctx);
 /**
  * aio_timer_new_with_attrs:
  * @ctx: the aio context
diff --git a/include/block/raw-aio.h b/include/block/raw-aio.h
index ba223dd1f1..1885b086e6 100644
--- a/include/block/raw-aio.h
+++ b/include/block/raw-aio.h
@@ -58,6 +58,18 @@ void laio_attach_aio_context(LinuxAioState *s, AioContext *new_context);
 void laio_io_plug(BlockDriverState *bs, LinuxAioState *s);
 void laio_io_unplug(BlockDriverState *bs, LinuxAioState *s);
 #endif
+/* io_uring.c - Linux io_uring implementation */
+#ifdef CONFIG_LINUX_IO_URING
+typedef struct LuringState LuringState;
+LuringState *luring_init(Error **errp);
+void luring_cleanup(LuringState *s);
+int coroutine_fn luring_co_submit(BlockDriverState *bs, LuringState *s, 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);
+void luring_io_plug(BlockDriverState *bs, LuringState *s);
+void luring_io_unplug(BlockDriverState *bs, LuringState *s);
+#endif
 
 #ifdef _WIN32
 typedef struct QEMUWin32AIOState QEMUWin32AIOState;
-- 
2.17.1

[Qemu-devel] [PATCH v4 5/9] stubs: add stubs for io_uring interface

[Aarushi Mehta]

Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 MAINTAINERS         |  1 +
 stubs/Makefile.objs |  1 +
 stubs/io_uring.c    | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 34 insertions(+)
 create mode 100644 stubs/io_uring.c

diff --git a/MAINTAINERS b/MAINTAINERS
index dcaddec21f..e30f62024e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2521,6 +2521,7 @@ R: Stefan Hajnoczi <stefan@redhat.com>
 L: qemu-block@nongnu.org
 S: Maintained
 F: block/io_uring.c
+F: stubs/io_uring.c
 
 qcow2
 M: Kevin Wolf <kwolf@redhat.com>
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 9c7393b08c..5cf160a9c8 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -13,6 +13,7 @@ stub-obj-y += iothread.o
 stub-obj-y += iothread-lock.o
 stub-obj-y += is-daemonized.o
 stub-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
+stub-obj-$(CONFIG_LINUX_IO_URING) += io_uring.o
 stub-obj-y += machine-init-done.o
 stub-obj-y += migr-blocker.o
 stub-obj-y += change-state-handler.o
diff --git a/stubs/io_uring.c b/stubs/io_uring.c
new file mode 100644
index 0000000000..622d1e4648
--- /dev/null
+++ b/stubs/io_uring.c
@@ -0,0 +1,32 @@
+/*
+ * Linux io_uring support.
+ *
+ * Copyright (C) 2009 IBM, Corp.
+ * Copyright (C) 2009 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+#include "qemu/osdep.h"
+#include "block/aio.h"
+#include "block/raw-aio.h"
+
+void luring_detach_aio_context(LuringState *s, AioContext *old_context)
+{
+    abort();
+}
+
+void luring_attach_aio_context(LuringState *s, AioContext *new_context)
+{
+    abort();
+}
+
+LuringState *luring_init(Error **errp)
+{
+    abort();
+}
+
+void luring_cleanup(LuringState *s)
+{
+    abort();
+}
-- 
2.17.1

[Qemu-devel] [PATCH v4 6/9] util/async: add aio interfaces for io_uring

[Aarushi Mehta]

Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 util/async.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/util/async.c b/util/async.c
index c10642a385..2709f0edc3 100644
--- a/util/async.c
+++ b/util/async.c
@@ -277,6 +277,14 @@ aio_ctx_finalize(GSource     *source)
     }
 #endif
 
+#ifdef CONFIG_LINUX_IO_URING
+    if (ctx->linux_io_uring) {
+        luring_detach_aio_context(ctx->linux_io_uring, ctx);
+        luring_cleanup(ctx->linux_io_uring);
+        ctx->linux_io_uring = NULL;
+    }
+#endif
+
     assert(QSLIST_EMPTY(&ctx->scheduled_coroutines));
     qemu_bh_delete(ctx->co_schedule_bh);
 
@@ -341,6 +349,29 @@ LinuxAioState *aio_get_linux_aio(AioContext *ctx)
 }
 #endif
 
+#ifdef CONFIG_LINUX_IO_URING
+LuringState *aio_setup_linux_io_uring(AioContext *ctx, Error **errp)
+{
+    if (ctx->linux_io_uring) {
+        return ctx->linux_io_uring;
+    }
+
+    ctx->linux_io_uring = luring_init(errp);
+    if (!ctx->linux_io_uring) {
+        return NULL;
+    }
+
+    luring_attach_aio_context(ctx->linux_io_uring, ctx);
+    return ctx->linux_io_uring;
+}
+
+LuringState *aio_get_linux_io_uring(AioContext *ctx)
+{
+    assert(ctx->linux_io_uring);
+    return ctx->linux_io_uring;
+}
+#endif
+
 void aio_notify(AioContext *ctx)
 {
     /* Write e.g. bh->scheduled before reading ctx->notify_me.  Pairs
@@ -432,6 +463,11 @@ AioContext *aio_context_new(Error **errp)
 #ifdef CONFIG_LINUX_AIO
     ctx->linux_aio = NULL;
 #endif
+
+#ifdef CONFIG_LINUX_IO_URING
+    ctx->linux_io_uring = NULL;
+#endif
+
     ctx->thread_pool = NULL;
     qemu_rec_mutex_init(&ctx->lock);
     timerlistgroup_init(&ctx->tlg, aio_timerlist_notify, ctx);
-- 
2.17.1

[Qemu-devel] [PATCH v4 7/9] blockdev: accept io_uring as option

[Aarushi Mehta]

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 blockdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c
index 17c2d801d7..58a9e69268 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -386,6 +386,8 @@ static void extract_common_blockdev_options(QemuOpts *opts, int *bdrv_flags,
         if ((aio = qemu_opt_get(opts, "aio")) != NULL) {
             if (!strcmp(aio, "native")) {
                 *bdrv_flags |= BDRV_O_NATIVE_AIO;
+            } else if (!strcmp(aio, "io_uring")) {
+                *bdrv_flags |= BDRV_O_IO_URING;
             } else if (!strcmp(aio, "threads")) {
                 /* this is the default */
             } else {
@@ -4568,7 +4570,7 @@ QemuOptsList qemu_common_drive_opts = {
         },{
             .name = "aio",
             .type = QEMU_OPT_STRING,
-            .help = "host AIO implementation (threads, native)",
+            .help = "host AIO implementation (threads, native, io_uring)",
         },{
             .name = BDRV_OPT_CACHE_WB,
             .type = QEMU_OPT_BOOL,
-- 
2.17.1

[Qemu-devel] [PATCH v4 8/9] block/file-posix.c: extend to use io_uring

[Aarushi Mehta]

Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 block/file-posix.c | 85 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 69 insertions(+), 16 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index d018429672..211dfe5337 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -154,6 +154,7 @@ typedef struct BDRVRawState {
     bool has_write_zeroes:1;
     bool discard_zeroes:1;
     bool use_linux_aio:1;
+    bool use_linux_io_uring:1;
     bool page_cache_inconsistent:1;
     bool has_fallocate;
     bool needs_alignment;
@@ -423,7 +424,7 @@ static QemuOptsList raw_runtime_opts = {
         {
             .name = "aio",
             .type = QEMU_OPT_STRING,
-            .help = "host AIO implementation (threads, native)",
+            .help = "host AIO implementation (threads, native, io_uring)",
         },
         {
             .name = "locking",
@@ -482,9 +483,15 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
         goto fail;
     }
 
-    aio_default = (bdrv_flags & BDRV_O_NATIVE_AIO)
-                  ? BLOCKDEV_AIO_OPTIONS_NATIVE
-                  : BLOCKDEV_AIO_OPTIONS_THREADS;
+    if (bdrv_flags & BDRV_O_NATIVE_AIO) {
+        aio_default = BLOCKDEV_AIO_OPTIONS_NATIVE;
+#ifdef CONFIG_LINUX_IO_URING
+    } else if (bdrv_flags & BDRV_O_IO_URING) {
+        aio_default = BLOCKDEV_AIO_OPTIONS_IO_URING;
+#endif
+    } else {
+        aio_default = BLOCKDEV_AIO_OPTIONS_THREADS;
+    }
     aio = qapi_enum_parse(&BlockdevAioOptions_lookup,
                           qemu_opt_get(opts, "aio"),
                           aio_default, &local_err);
@@ -493,7 +500,11 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
         ret = -EINVAL;
         goto fail;
     }
+
     s->use_linux_aio = (aio == BLOCKDEV_AIO_OPTIONS_NATIVE);
+#ifdef CONFIG_LINUX_IO_URING
+    s->use_linux_io_uring = (aio == BLOCKDEV_AIO_OPTIONS_IO_URING);
+#endif
 
     locking = qapi_enum_parse(&OnOffAuto_lookup,
                               qemu_opt_get(opts, "locking"),
@@ -557,7 +568,7 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
     s->shared_perm = BLK_PERM_ALL;
 
 #ifdef CONFIG_LINUX_AIO
-     /* Currently Linux does AIO only for files opened with O_DIRECT */
+    /* Currently Linux does AIO only for files opened with O_DIRECT */
     if (s->use_linux_aio) {
         if (!(s->open_flags & O_DIRECT)) {
             error_setg(errp, "aio=native was specified, but it requires "
@@ -579,6 +590,22 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
     }
 #endif /* !defined(CONFIG_LINUX_AIO) */
 
+#ifdef CONFIG_LINUX_IO_URING
+    if (s->use_linux_io_uring) {
+        if (!aio_setup_linux_io_uring(bdrv_get_aio_context(bs), errp)) {
+            error_prepend(errp, "Unable to use io_uring: ");
+            goto fail;
+        }
+    }
+#else
+    if (s->use_linux_io_uring) {
+        error_setg(errp, "aio=io_uring was specified, but is not supported "
+                         "in this build.");
+        ret = -EINVAL;
+        goto fail;
+    }
+#endif /* !defined(CONFIG_LINUX_IO_URING) */
+
     s->has_discard = true;
     s->has_write_zeroes = true;
     if ((bs->open_flags & BDRV_O_NOCACHE) != 0) {
@@ -1875,16 +1902,20 @@ static int coroutine_fn raw_co_prw(BlockDriverState *bs, uint64_t offset,
      * If this is the case tell the low-level driver that it needs
      * to copy the buffer.
      */
-    if (s->needs_alignment) {
-        if (!bdrv_qiov_is_aligned(bs, qiov)) {
-            type |= QEMU_AIO_MISALIGNED;
+    if (s->needs_alignment && !bdrv_qiov_is_aligned(bs, qiov)) {
+                type |= QEMU_AIO_MISALIGNED;
+#ifdef CONFIG_LINUX_IO_URING
+    } else if (s->use_linux_io_uring) {
+        LuringState *aio = aio_get_linux_io_uring(bdrv_get_aio_context(bs));
+        assert(qiov->size == bytes);
+        return luring_co_submit(bs, aio, s->fd, offset, qiov, type);
+#endif
 #ifdef CONFIG_LINUX_AIO
-        } else if (s->use_linux_aio) {
-            LinuxAioState *aio = aio_get_linux_aio(bdrv_get_aio_context(bs));
-            assert(qiov->size == bytes);
-            return laio_co_submit(bs, aio, s->fd, offset, qiov, type);
+    } else if (s->use_linux_aio && s->needs_alignment) {
+        LinuxAioState *aio = aio_get_linux_aio(bdrv_get_aio_context(bs));
+        assert(qiov->size == bytes);
+        return laio_co_submit(bs, aio, s->fd, offset, qiov, type);
 #endif
-        }
     }
 
     acb = (RawPosixAIOData) {
@@ -1920,24 +1951,36 @@ static int coroutine_fn raw_co_pwritev(BlockDriverState *bs, uint64_t offset,
 
 static void raw_aio_plug(BlockDriverState *bs)
 {
+    BDRVRawState __attribute__((unused)) *s = bs->opaque;
 #ifdef CONFIG_LINUX_AIO
-    BDRVRawState *s = bs->opaque;
     if (s->use_linux_aio) {
         LinuxAioState *aio = aio_get_linux_aio(bdrv_get_aio_context(bs));
         laio_io_plug(bs, aio);
     }
 #endif
+#ifdef CONFIG_LINUX_IO_URING
+    if (s->use_linux_io_uring) {
+        LuringState *aio = aio_get_linux_io_uring(bdrv_get_aio_context(bs));
+        luring_io_plug(bs, aio);
+    }
+#endif
 }
 
 static void raw_aio_unplug(BlockDriverState *bs)
 {
+    BDRVRawState __attribute__((unused)) *s = bs->opaque;
 #ifdef CONFIG_LINUX_AIO
-    BDRVRawState *s = bs->opaque;
     if (s->use_linux_aio) {
         LinuxAioState *aio = aio_get_linux_aio(bdrv_get_aio_context(bs));
         laio_io_unplug(bs, aio);
     }
 #endif
+#ifdef CONFIG_LINUX_IO_URING
+    if (s->use_linux_io_uring) {
+        LuringState *aio = aio_get_linux_io_uring(bdrv_get_aio_context(bs));
+        luring_io_unplug(bs, aio);
+    }
+#endif
 }
 
 static int raw_co_flush_to_disk(BlockDriverState *bs)
@@ -1963,8 +2006,8 @@ static int raw_co_flush_to_disk(BlockDriverState *bs)
 static void raw_aio_attach_aio_context(BlockDriverState *bs,
                                        AioContext *new_context)
 {
+    BDRVRawState __attribute__((unused)) *s = bs->opaque;
 #ifdef CONFIG_LINUX_AIO
-    BDRVRawState *s = bs->opaque;
     if (s->use_linux_aio) {
         Error *local_err;
         if (!aio_setup_linux_aio(new_context, &local_err)) {
@@ -1974,6 +2017,16 @@ static void raw_aio_attach_aio_context(BlockDriverState *bs,
         }
     }
 #endif
+#ifdef CONFIG_LINUX_IO_URING
+    if (s->use_linux_io_uring) {
+        Error *local_err;
+        if (!aio_setup_linux_io_uring(new_context, &local_err)) {
+            error_reportf_err(local_err, "Unable to use linux io_uring, "
+                                         "falling back to thread pool: ");
+            s->use_linux_io_uring = false;
+        }
+    }
+#endif
 }
 
 static void raw_close(BlockDriverState *bs)
-- 
2.17.1

[Qemu-devel] [PATCH v4 9/9] block: add trace events for io_uring

[Aarushi Mehta]

Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
---
 block/io_uring.c   | 14 ++++++++++++--
 block/trace-events |  8 ++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/block/io_uring.c b/block/io_uring.c
index 536a9fbe87..e92e45ccca 100644
--- a/block/io_uring.c
+++ b/block/io_uring.c
@@ -17,6 +17,7 @@
 #include "block/raw-aio.h"
 #include "qemu/coroutine.h"
 #include "qapi/error.h"
+#include "trace.h"
 
 #define MAX_EVENTS 128
 
@@ -192,12 +193,15 @@ static int ioq_submit(LuringState *s)
 
 void luring_io_plug(BlockDriverState *bs, LuringState *s)
 {
+    trace_luring_io_plug();
     s->io_q.plugged++;
 }
 
 void luring_io_unplug(BlockDriverState *bs, LuringState *s)
 {
     assert(s->io_q.plugged);
+    trace_luring_io_unplug(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) {
         ioq_submit(s);
@@ -218,6 +222,7 @@ void luring_io_unplug(BlockDriverState *bs, LuringState *s)
 static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
                             uint64_t offset, int type)
 {
+    int ret;
     struct io_uring_sqe *sqes = io_uring_get_sqe(&s->ring);
     if (!sqes) {
         sqes = &luringcb->sqeq;
@@ -243,11 +248,14 @@ static int luring_do_submit(int fd, LuringAIOCB *luringcb, LuringState *s,
     }
     io_uring_sqe_set_data(sqes, luringcb);
     s->io_q.in_queue++;
-
+    trace_luring_do_submit(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_EVENTS)) {
-        return ioq_submit(s);
+        ret = ioq_submit(s);
+        trace_luring_do_submit_done(ret);
+        return ret;
     }
     return 0;
 }
@@ -295,6 +303,7 @@ LuringState *luring_init(Error **errp)
     int rc;
     LuringState *s;
     s = g_malloc0(sizeof(*s));
+    trace_luring_init_state((void *)s, sizeof(*s));
     struct io_uring *ring = &s->ring;
     rc =  io_uring_queue_init(MAX_EVENTS, ring, 0);
     if (rc < 0) {
@@ -312,4 +321,5 @@ void luring_cleanup(LuringState *s)
 {
     io_uring_queue_exit(&s->ring);
     g_free(s);
+    trace_luring_cleanup_state();
 }
diff --git a/block/trace-events b/block/trace-events
index 1e0653ce6d..038ff14815 100644
--- a/block/trace-events
+++ b/block/trace-events
@@ -60,6 +60,14 @@ qmp_block_stream(void *bs, void *job) "bs %p job %p"
 file_paio_submit(void *acb, void *opaque, int64_t offset, int count, int type) "acb %p opaque %p offset %"PRId64" count %d type %d"
 file_copy_file_range(void *bs, int src, int64_t src_off, int dst, int64_t dst_off, int64_t bytes, int flags, int64_t ret) "bs %p src_fd %d offset %"PRIu64" dst_fd %d offset %"PRIu64" bytes %"PRIu64" flags %d ret %"PRId64
 
+#io_uring.c
+luring_init_state(void *s, size_t size) "s %p size %zu"
+luring_cleanup_state(void) "s freed"
+disable luring_io_plug(void) "plug"
+disable luring_io_unplug(int blocked, int plugged, int queued, int inflight) "blocked %d plugged %d queued %d inflight %d"
+disable luring_do_submit(int blocked, int plugged, int queued, int inflight) "blocked %d plugged %d queued %d inflight %d"
+disable luring_do_submit_done(int ret) "submitted to kernel %d"
+
 # qcow2.c
 qcow2_writev_start_req(void *co, int64_t offset, int bytes) "co %p offset 0x%" PRIx64 " bytes %d"
 qcow2_writev_done_req(void *co, int ret) "co %p ret %d"
-- 
2.17.1

Re: [Qemu-devel] [PATCH v4 2/9] qapi/block-core: add option for io_uring

[Markus Armbruster]

Aarushi Mehta <mehta.aaru20@gmail.com> writes:

> Option only enumerates for hosts that support it.

Blank line here, please.  Same in other patches.

> Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
> ---
>  qapi/block-core.json | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 1defcde048..db7eedd058 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2792,11 +2792,13 @@
>  #
>  # @threads:     Use qemu's thread pool
>  # @native:      Use native AIO backend (only Linux and Windows)
> +# @io_uring:    Use linux io_uring (since 4.1)
>  #
>  # Since: 2.9
>  ##
>  { 'enum': 'BlockdevAioOptions',
> -  'data': [ 'threads', 'native' ] }
> +  'data': [ 'threads', 'native',
> +            { 'name': 'io_uring', 'if': 'defined(CONFIG_LINUX_IO_URING)' } ] }

We prefer '-' over '_' in the QAPI schema: 'io-uring' instead of
'io_uring'.  Exceptions can be made when existing siblings use '_' (not
the case here), or to match how the thing is commonly spelled outside
QEMU.  Up to the subject matter experts; I just want to make sure it's
not accidental.

>  
>  ##
>  # @BlockdevCacheOptions:

Re: [Qemu-devel] [Qemu-block] [PATCH v4 1/9] configure: permit use of io_uring

[Maxim Levitsky]

On Mon, 2019-06-03 at 18:08 +0530, Aarushi Mehta wrote:
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
> ---
>  configure | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/configure b/configure
> index 6cdcfb2dc3..cb49ef0fcc 100755
> --- a/configure
> +++ b/configure
> @@ -365,6 +365,7 @@ xen=""
>  xen_ctrl_version=""
>  xen_pci_passthrough=""
>  linux_aio=""
> +linux_io_uring=""
>  cap_ng=""
>  attr=""
>  libattr=""
> @@ -1266,6 +1267,10 @@ for opt do
>    ;;
>    --enable-linux-aio) linux_aio="yes"
>    ;;
> +  --disable-linux-io-uring) linux_io_uring="no"
> +  ;;
> +  --enable-linux-io-uring) linux_io_uring="yes"
> +  ;;
>    --disable-attr) attr="no"
>    ;;
>    --enable-attr) attr="yes"
> @@ -1784,6 +1789,7 @@ disabled with --disable-FEATURE, default is enabled if available:
>    vde             support for vde network
>    netmap          support for netmap network
>    linux-aio       Linux AIO support
> +  linux-io-uring  Linux io_uring support
>    cap-ng          libcap-ng support
>    attr            attr and xattr support
>    vhost-net       vhost-net kernel acceleration support
> @@ -3973,6 +3979,21 @@ EOF
>      linux_aio=no
>    fi
>  fi
> +##########################################
> +# linux-io-uring probe
> +
> +if test "$linux_io_uring" != "no" ; then
> +  if $pkg_config liburing; then
> +    linux_io_uring_cflags=$($pkg_config --cflags liburing)
> +    linux_io_uring_libs=$($pkg_config --libs liburing)
> +    linux_io_uring=yes
> +  else
> +    if test "$linux_io_uring" = "yes" ; then
> +      feature_not_found "linux io_uring" "Install liburing devel"
> +    fi
> +    linux_io_uring=no
> +  fi
> +fi
>  
>  ##########################################
>  # TPM emulation is only on POSIX
> @@ -6396,6 +6417,7 @@ echo "PIE               $pie"
>  echo "vde support       $vde"
>  echo "netmap support    $netmap"
>  echo "Linux AIO support $linux_aio"
> +echo "Linux io_uring support $linux_io_uring"
>  echo "ATTR/XATTR support $attr"
>  echo "Install blobs     $blobs"
>  echo "KVM support       $kvm"
> @@ -6876,6 +6898,11 @@ fi
>  if test "$linux_aio" = "yes" ; then
>    echo "CONFIG_LINUX_AIO=y" >> $config_host_mak
>  fi
> +if test "$linux_io_uring" = "yes" ; then
> +  echo "CONFIG_LINUX_IO_URING=y" >> $config_host_mak
> +  echo "LINUX_IO_URING_CFLAGS=$linux_io_uring_cflags" >> $config_host_mak
> +  echo "LINUX_IO_URING_LIBS=$linux_io_uring_libs" >> $config_host_mak
> +fi
>  if test "$attr" = "yes" ; then
>    echo "CONFIG_ATTR=y" >> $config_host_mak
>  fi



Reviewed-by: Maxim Levitsky <maximlevitsky@gmail.com>

Best regards,
	Maxim Levitsky

Re: [Qemu-devel] [Qemu-block] [PATCH v4 2/9] qapi/block-core: add option for io_uring

[Maxim Levitsky]

On Wed, 2019-06-05 at 07:58 +0200, Markus Armbruster wrote:
> Aarushi Mehta <mehta.aaru20@gmail.com> writes:
> 
> > Option only enumerates for hosts that support it.
> 
> Blank line here, please.  Same in other patches.
> 
> > Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
> > ---
> >  qapi/block-core.json | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index 1defcde048..db7eedd058 100644
> > --- a/qapi/block-core.json
> > +++ b/qapi/block-core.json
> > @@ -2792,11 +2792,13 @@
> >  #
> >  # @threads:     Use qemu's thread pool
> >  # @native:      Use native AIO backend (only Linux and Windows)
> > +# @io_uring:    Use linux io_uring (since 4.1)
> >  #
> >  # Since: 2.9
> >  ##
> >  { 'enum': 'BlockdevAioOptions',
> > -  'data': [ 'threads', 'native' ] }
> > +  'data': [ 'threads', 'native',
> > +            { 'name': 'io_uring', 'if': 'defined(CONFIG_LINUX_IO_URING)' } ] }
> 
> We prefer '-' over '_' in the QAPI schema: 'io-uring' instead of
> 'io_uring'.  Exceptions can be made when existing siblings use '_' (not
> the case here), or to match how the thing is commonly spelled outside
> QEMU.  Up to the subject matter experts; I just want to make sure it's
> not accidental

I agree with that.
Other than that,

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky

Re: [Qemu-devel] [Qemu-block] [PATCH v4 3/9] block/block: add BDRV flag for io_uring

[Maxim Levitsky]

On Mon, 2019-06-03 at 18:08 +0530, Aarushi Mehta wrote:
> Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/block/block.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/block/block.h b/include/block/block.h
> index 9b083e2bca..60f7c6c01c 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -121,6 +121,7 @@ typedef struct HDGeometry {
>                                        ignoring the format layer */
>  #define BDRV_O_NO_IO       0x10000 /* don't initialize for I/O */
>  #define BDRV_O_AUTO_RDONLY 0x20000 /* degrade to read-only if opening read-write fails */
> +#define BDRV_O_IO_URING    0x40000 /* use io_uring instead of the thread pool */
>  
>  #define BDRV_O_CACHE_MASK  (BDRV_O_NOCACHE | BDRV_O_NO_FLUSH)
>  

I had some fun learning now why do we need that flag.
Lot of code could be removed when someday we will remove the -drive interface.


Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky

Re: [Qemu-devel] [PATCH v4 0/9] Add support for io_uring

[Sergio Lopez]

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Aarushi Mehta <mehta.aaru20@gmail.com> writes:

> This patch series adds support for the newly developed io_uring Linux AIO
> interface. Linux io_uring is faster than Linux's AIO asynchronous I/O code,
> offers efficient buffered asynchronous I/O support, the ability to do I/O
> without performing a system call via polled I/O, and other efficiency enhancements.
>
> Testing it requires a host kernel (5.1+) and the liburing library.
> Use the option -drive aio=io_uring to enable it.
>
> v4:
> - Add error handling
> - Add trace events
> - Remove aio submission based code
>
> v3:
> - Fix major errors in io_uring (sorry)
> - Option now enumerates for CONFIG_LINUX_IO_URING
> - pkg config support added
>
> Aarushi Mehta (9):
>   configure: permit use of io_uring
>   qapi/block-core: add option for io_uring
>   block/block: add BDRV flag for io_uring
>   block/io_uring: implements interfaces for io_uring
>   stubs: add stubs for io_uring interface
>   util/async: add aio interfaces for io_uring
>   blockdev: accept io_uring as option
>   block/file-posix.c: extend to use io_uring
>   block: add trace events for io_uring
>
>  MAINTAINERS             |   8 +
>  block/Makefile.objs     |   3 +
>  block/file-posix.c      |  85 +++++++++--
>  block/io_uring.c        | 325 ++++++++++++++++++++++++++++++++++++++++
>  block/trace-events      |   8 +
>  blockdev.c              |   4 +-
>  configure               |  27 ++++
>  include/block/aio.h     |  16 +-
>  include/block/block.h   |   1 +
>  include/block/raw-aio.h |  12 ++
>  qapi/block-core.json    |   4 +-
>  stubs/Makefile.objs     |   1 +
>  stubs/io_uring.c        |  32 ++++
>  util/async.c            |  36 +++++
>  14 files changed, 543 insertions(+), 19 deletions(-)
>  create mode 100644 block/io_uring.c
>  create mode 100644 stubs/io_uring.c

Hi Aarushi,

I gave this version of the patchset a try, and found that IO hangs when
the device is assigned to an IOThread. Sometimes is able to serve a few
requests getting through the Guest OS boot process, to hang the moment
you try generate some IO on the device, while others it hangs when Linux
tries to read the partitions from the device.

I'm starting QEMU this way:

./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -name rhel80,debug-threads=on -m 2g -smp 4 -object iothread,id=iothread0 -blockdev node-name=rhel80,driver=qcow2,file.driver=file,file.filename=/home/VirtualMachines/rhel80.qcow2 -device virtio-blk,drive=rhel80 -serial tcp::6667,server,nowait -qmp tcp::6668,server,nowait -nographic -net user,hostfwd=tcp::6666-:22 -net nic,model=virtio -device virtio-rng -drive file=/dev/nullb0,format=raw,cache=none,aio=io_uring,if=none,id=test -device virtio-blk,drive=test,iothread=iothread0

Could you please take a look at this issue?

Thanks,
Sergio.

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Re: [Qemu-devel] [PATCH v4 2/9] qapi/block-core: add option for io_uring

[Stefan Hajnoczi]

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On Wed, Jun 05, 2019 at 07:58:32AM +0200, Markus Armbruster wrote:
> Aarushi Mehta <mehta.aaru20@gmail.com> writes:
> 
> > Option only enumerates for hosts that support it.
> 
> Blank line here, please.  Same in other patches.
> 
> > Signed-off-by: Aarushi Mehta <mehta.aaru20@gmail.com>
> > ---
> >  qapi/block-core.json | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/qapi/block-core.json b/qapi/block-core.json
> > index 1defcde048..db7eedd058 100644
> > --- a/qapi/block-core.json
> > +++ b/qapi/block-core.json
> > @@ -2792,11 +2792,13 @@
> >  #
> >  # @threads:     Use qemu's thread pool
> >  # @native:      Use native AIO backend (only Linux and Windows)
> > +# @io_uring:    Use linux io_uring (since 4.1)
> >  #
> >  # Since: 2.9
> >  ##
> >  { 'enum': 'BlockdevAioOptions',
> > -  'data': [ 'threads', 'native' ] }
> > +  'data': [ 'threads', 'native',
> > +            { 'name': 'io_uring', 'if': 'defined(CONFIG_LINUX_IO_URING)' } ] }
> 
> We prefer '-' over '_' in the QAPI schema: 'io-uring' instead of
> 'io_uring'.  Exceptions can be made when existing siblings use '_' (not
> the case here), or to match how the thing is commonly spelled outside
> QEMU.  Up to the subject matter experts; I just want to make sure it's
> not accidental.

#2

The Linux API is called "io_uring".  That's the commonly used name for
it, not io-uring, IOURing, etc.  The QMP schema has the ability to
represent the official spelling, so I think we should use it for this
enum value.

Stefan

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Re: [Qemu-devel] [PATCH v4 4/9] block/io_uring: implements interfaces for io_uring

[Stefan Hajnoczi]

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On Mon, Jun 03, 2019 at 06:08:18PM +0530, Aarushi Mehta wrote:
> +static void qemu_luring_process_completions(LuringState *s)
> +{
> +    struct io_uring_cqe *cqes;
> +    int ret;
> +
> +    /*
> +     * Request completion callbacks can run the nested event loop.
> +     * Schedule ourselves so the nested event loop will "see" remaining
> +     * completed requests and process them.  Without this, completion
> +     * callbacks that wait for other requests using a nested event loop
> +     * would hang forever.
> +     */
> +    qemu_bh_schedule(s->completion_bh);
> +
> +    while (io_uring_peek_cqe(&s->ring, &cqes) == 0) {
> +        if (!cqes) {
> +            break;
> +        }
> +        LuringAIOCB *luringcb = io_uring_cqe_get_data(cqes);
> +        read_barrier();

What is the purpose of this barrier?

> +static void qemu_luring_process_completions_and_submit(LuringState *s)
> +{
> +    aio_context_acquire(s->aio_context);
> +    qemu_luring_process_completions(s);
> +
> +    if (!s->io_q.plugged && !s->io_q.in_queue) {

Submit when there are queued requesting waiting for submission:

s/!s->io_q.in_queue/s->io_q.in_queue > 0/

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Re: [Qemu-devel] [PATCH v4 0/9] Add support for io_uring

[Stefan Hajnoczi]

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On Fri, Jun 07, 2019 at 12:59:54PM +0200, Sergio Lopez wrote:
> I gave this version of the patchset a try, and found that IO hangs when
> the device is assigned to an IOThread. Sometimes is able to serve a few
> requests getting through the Guest OS boot process, to hang the moment
> you try generate some IO on the device, while others it hangs when Linux
> tries to read the partitions from the device.
> 
> I'm starting QEMU this way:
> 
> ./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -name rhel80,debug-threads=on -m 2g -smp 4 -object iothread,id=iothread0 -blockdev node-name=rhel80,driver=qcow2,file.driver=file,file.filename=/home/VirtualMachines/rhel80.qcow2 -device virtio-blk,drive=rhel80 -serial tcp::6667,server,nowait -qmp tcp::6668,server,nowait -nographic -net user,hostfwd=tcp::6666-:22 -net nic,model=virtio -device virtio-rng -drive file=/dev/nullb0,format=raw,cache=none,aio=io_uring,if=none,id=test -device virtio-blk,drive=test,iothread=iothread0
> 
> Could you please take a look at this issue?

Maybe the ioq_submit() issue I mentioned solves this.

Stefan

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Re: [Qemu-devel] [PATCH v4 0/9] Add support for io_uring

[Stefan Hajnoczi]

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On Fri, Jun 07, 2019 at 12:59:54PM +0200, Sergio Lopez wrote:
> I gave this version of the patchset a try, and found that IO hangs when
> the device is assigned to an IOThread. Sometimes is able to serve a few
> requests getting through the Guest OS boot process, to hang the moment
> you try generate some IO on the device, while others it hangs when Linux
> tries to read the partitions from the device.
> 
> I'm starting QEMU this way:
> 
> ./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -name rhel80,debug-threads=on -m 2g -smp 4 -object iothread,id=iothread0 -blockdev node-name=rhel80,driver=qcow2,file.driver=file,file.filename=/home/VirtualMachines/rhel80.qcow2 -device virtio-blk,drive=rhel80 -serial tcp::6667,server,nowait -qmp tcp::6668,server,nowait -nographic -net user,hostfwd=tcp::6666-:22 -net nic,model=virtio -device virtio-rng -drive file=/dev/nullb0,format=raw,cache=none,aio=io_uring,if=none,id=test -device virtio-blk,drive=test,iothread=iothread0
> 
> Could you please take a look at this issue?

BTW I was referring to the inverted logic where qemu_luring_process_completions_and_submit() fails to call ioq_submit().

Stefan

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Re: [Qemu-devel] [PATCH v4 0/9] Add support for io_uring

[Sergio Lopez]

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Stefan Hajnoczi <stefanha@redhat.com> writes:

> On Fri, Jun 07, 2019 at 12:59:54PM +0200, Sergio Lopez wrote:
>> I gave this version of the patchset a try, and found that IO hangs when
>> the device is assigned to an IOThread. Sometimes is able to serve a few
>> requests getting through the Guest OS boot process, to hang the moment
>> you try generate some IO on the device, while others it hangs when Linux
>> tries to read the partitions from the device.
>> 
>> I'm starting QEMU this way:
>> 
>> ./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -name rhel80,debug-threads=on -m 2g -smp 4 -object iothread,id=iothread0 -blockdev node-name=rhel80,driver=qcow2,file.driver=file,file.filename=/home/VirtualMachines/rhel80.qcow2 -device virtio-blk,drive=rhel80 -serial tcp::6667,server,nowait -qmp tcp::6668,server,nowait -nographic -net user,hostfwd=tcp::6666-:22 -net nic,model=virtio -device virtio-rng -drive file=/dev/nullb0,format=raw,cache=none,aio=io_uring,if=none,id=test -device virtio-blk,drive=test,iothread=iothread0
>> 
>> Could you please take a look at this issue?
>
> BTW I was referring to the inverted logic where qemu_luring_process_completions_and_submit() fails to call ioq_submit().

Yes, that was the problem.

Sergio.

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