[Qemu-devel] [RFC v2 0/6] dataplane: switch to N:M devices-per-thread model

[Qemu-devel] [RFC v2 0/6] dataplane: switch to N:M devices-per-thread model

[Stefan Hajnoczi]

This series moves the event loop thread out of dataplane code.  It makes
-object iothread,id=foo a separate concept.  This makes it possible to bind
several devices to the same iothread.

Syntax:

  qemu -object iothread,id=iothread0 \
       -device virtio-blk-pci,iothread=iothread0,x-data-plane=on,...

For backwards-compatibility the iothread= parameter can be omitted.  A
per-device IOThread will be created behind the scenes (just like the old 1:1
threading model).

This series includes the aio_context_acquire/release API which makes it easy to
synchronize access to AioContext across threads.

Mike: My goal is to get this into QEMU 2.0.  How can we get the QContext ball
rolling?  The only feature I'm missing is an API to query thread IDs for
iothread host CPU affinity.  Besides that the IOThread object does what I need
for virtio-blk dataplane.

v2:
 * Based off Igor's "-object/object-add support custom location and 2nd stage
   initialization" series
 * Dropped dedicated -iothread option in favor of -object
 * Avoid re-acquiring rfifo in iothread_run() [mdroth]

Stefan Hajnoczi (6):
  rfifolock: add recursive FIFO lock
  aio: add aio_context_acquire() and aio_context_release()
  iothread: add I/O thread object
  qdev: add get_pointer_and_free() for temporary strings
  iothread: add "iothread" qdev property type
  dataplane: replace internal thread with IOThread

 Makefile.objs                    |   1 +
 async.c                          |  18 ++++++
 hw/block/dataplane/virtio-blk.c  |  95 +++++++++++++++-------------
 hw/core/qdev-properties-system.c |  65 +++++++++++++++++++
 include/block/aio.h              |  18 ++++++
 include/hw/qdev-properties.h     |   3 +
 include/hw/virtio/virtio-blk.h   |   8 ++-
 include/qemu/rfifolock.h         |  54 ++++++++++++++++
 include/sysemu/iothread.h        |  30 +++++++++
 iothread.c                       | 132 +++++++++++++++++++++++++++++++++++++++
 tests/Makefile                   |   2 +
 tests/test-aio.c                 |  58 +++++++++++++++++
 tests/test-rfifolock.c           |  90 ++++++++++++++++++++++++++
 util/Makefile.objs               |   1 +
 util/rfifolock.c                 |  78 +++++++++++++++++++++++
 15 files changed, 609 insertions(+), 44 deletions(-)
 create mode 100644 include/qemu/rfifolock.h
 create mode 100644 include/sysemu/iothread.h
 create mode 100644 iothread.c
 create mode 100644 tests/test-rfifolock.c
 create mode 100644 util/rfifolock.c

-- 
1.8.4.2

[Qemu-devel] [RFC v2 1/6] rfifolock: add recursive FIFO lock

[Stefan Hajnoczi]

QemuMutex does not guarantee fairness and cannot be acquired
recursively:

Fairness means each locker gets a turn and the scheduler cannot cause
starvation.

Recursive locking is useful for composition, it allows a sequence of
locking operations to be invoked atomically by acquiring the lock around
them.

This patch adds RFifoLock, a recursive lock that guarantees FIFO order.
Its first user is added in the next patch.

RFifoLock has one additional feature: it can be initialized with an
optional contention callback.  The callback is invoked whenever a thread
must wait for the lock.  For example, it can be used to poke the current
owner so that they release the lock soon.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/qemu/rfifolock.h | 54 +++++++++++++++++++++++++++++
 tests/Makefile           |  2 ++
 tests/test-rfifolock.c   | 90 ++++++++++++++++++++++++++++++++++++++++++++++++
 util/Makefile.objs       |  1 +
 util/rfifolock.c         | 78 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 225 insertions(+)
 create mode 100644 include/qemu/rfifolock.h
 create mode 100644 tests/test-rfifolock.c
 create mode 100644 util/rfifolock.c

diff --git a/include/qemu/rfifolock.h b/include/qemu/rfifolock.h
new file mode 100644
index 0000000..b23ab53
--- /dev/null
+++ b/include/qemu/rfifolock.h
@@ -0,0 +1,54 @@
+/*
+ * Recursive FIFO lock
+ *
+ * Copyright Red Hat, Inc. 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <stefanha@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef QEMU_RFIFOLOCK_H
+#define QEMU_RFIFOLOCK_H
+
+#include "qemu/thread.h"
+
+/* Recursive FIFO lock
+ *
+ * This lock provides more features than a plain mutex:
+ *
+ * 1. Fairness - enforces FIFO order.
+ * 2. Nesting - can be taken recursively.
+ * 3. Contention callback - optional, called when thread must wait.
+ *
+ * The recursive FIFO lock is heavyweight so prefer other synchronization
+ * primitives if you do not need its features.
+ */
+typedef struct {
+    QemuMutex lock;             /* protects all fields */
+
+    /* FIFO order */
+    unsigned int head;          /* active ticket number */
+    unsigned int tail;          /* waiting ticket number */
+    QemuCond cond;              /* used to wait for our ticket number */
+
+    /* Nesting */
+    QemuThread owner_thread;    /* thread that currently has ownership */
+    unsigned int nesting;       /* amount of nesting levels */
+
+    /* Contention callback */
+    void (*cb)(void *);         /* called when thread must wait, with ->lock
+                                 * held so it may not recursively lock/unlock
+                                 */
+    void *cb_opaque;
+} RFifoLock;
+
+void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque);
+void rfifolock_destroy(RFifoLock *r);
+void rfifolock_lock(RFifoLock *r);
+void rfifolock_unlock(RFifoLock *r);
+
+#endif /* QEMU_RFIFOLOCK_H */
diff --git a/tests/Makefile b/tests/Makefile
index 0b85a34..b1b3686 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -31,6 +31,7 @@ check-unit-y += tests/test-visitor-serialization$(EXESUF)
 check-unit-y += tests/test-iov$(EXESUF)
 gcov-files-test-iov-y = util/iov.c
 check-unit-y += tests/test-aio$(EXESUF)
+check-unit-y += tests/test-rfifolock$(EXESUF)
 check-unit-y += tests/test-throttle$(EXESUF)
 gcov-files-test-aio-$(CONFIG_WIN32) = aio-win32.c
 gcov-files-test-aio-$(CONFIG_POSIX) = aio-posix.c
@@ -153,6 +154,7 @@ tests/check-qjson$(EXESUF): tests/check-qjson.o libqemuutil.a libqemustub.a
 tests/check-qom-interface$(EXESUF): tests/check-qom-interface.o $(qom-core-obj) libqemuutil.a
 tests/test-coroutine$(EXESUF): tests/test-coroutine.o $(block-obj-y) libqemuutil.a libqemustub.a
 tests/test-aio$(EXESUF): tests/test-aio.o $(block-obj-y) libqemuutil.a libqemustub.a
+tests/test-rfifolock$(EXESUF): tests/test-rfifolock.o libqemuutil.a libqemustub.a
 tests/test-throttle$(EXESUF): tests/test-throttle.o $(block-obj-y) libqemuutil.a libqemustub.a
 tests/test-thread-pool$(EXESUF): tests/test-thread-pool.o $(block-obj-y) libqemuutil.a libqemustub.a
 tests/test-iov$(EXESUF): tests/test-iov.o libqemuutil.a
diff --git a/tests/test-rfifolock.c b/tests/test-rfifolock.c
new file mode 100644
index 0000000..440dbcb
--- /dev/null
+++ b/tests/test-rfifolock.c
@@ -0,0 +1,90 @@
+/*
+ * RFifoLock tests
+ *
+ * Copyright Red Hat, Inc. 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi    <stefanha@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ */
+
+#include <glib.h>
+#include "qemu-common.h"
+#include "qemu/rfifolock.h"
+
+static void test_nesting(void)
+{
+    RFifoLock lock;
+
+    /* Trivial test, ensure the lock is recursive */
+    rfifolock_init(&lock, NULL, NULL);
+    rfifolock_lock(&lock);
+    rfifolock_lock(&lock);
+    rfifolock_lock(&lock);
+    rfifolock_unlock(&lock);
+    rfifolock_unlock(&lock);
+    rfifolock_unlock(&lock);
+    rfifolock_destroy(&lock);
+}
+
+typedef struct {
+    RFifoLock lock;
+    int fd[2];
+} CallbackTestData;
+
+static void rfifolock_cb(void *opaque)
+{
+    CallbackTestData *data = opaque;
+    int ret;
+    char c = 0;
+
+    ret = write(data->fd[1], &c, sizeof(c));
+    g_assert(ret == 1);
+}
+
+static void *callback_thread(void *opaque)
+{
+    CallbackTestData *data = opaque;
+
+    /* The other thread holds the lock so the contention callback will be
+     * invoked...
+     */
+    rfifolock_lock(&data->lock);
+    rfifolock_unlock(&data->lock);
+    return NULL;
+}
+
+static void test_callback(void)
+{
+    CallbackTestData data;
+    QemuThread thread;
+    int ret;
+    char c;
+
+    rfifolock_init(&data.lock, rfifolock_cb, &data);
+    ret = qemu_pipe(data.fd);
+    g_assert(ret == 0);
+
+    /* Hold lock but allow the callback to kick us by writing to the pipe */
+    rfifolock_lock(&data.lock);
+    qemu_thread_create(&thread, callback_thread, &data, QEMU_THREAD_JOINABLE);
+    ret = read(data.fd[0], &c, sizeof(c));
+    g_assert(ret == 1);
+    rfifolock_unlock(&data.lock);
+    /* If we got here then the callback was invoked, as expected */
+
+    qemu_thread_join(&thread);
+    close(data.fd[0]);
+    close(data.fd[1]);
+    rfifolock_destroy(&data.lock);
+}
+
+int main(int argc, char **argv)
+{
+    g_test_init(&argc, &argv, NULL);
+    g_test_add_func("/nesting", test_nesting);
+    g_test_add_func("/callback", test_callback);
+    return g_test_run();
+}
diff --git a/util/Makefile.objs b/util/Makefile.objs
index af3e5cb..53a4c5e 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -13,3 +13,4 @@ util-obj-y += hexdump.o
 util-obj-y += crc32c.o
 util-obj-y += throttle.o
 util-obj-y += getauxval.o
+util-obj-y += rfifolock.o
diff --git a/util/rfifolock.c b/util/rfifolock.c
new file mode 100644
index 0000000..afbf748
--- /dev/null
+++ b/util/rfifolock.c
@@ -0,0 +1,78 @@
+/*
+ * Recursive FIFO lock
+ *
+ * Copyright Red Hat, Inc. 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <stefanha@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ *
+ */
+
+#include <assert.h>
+#include "qemu/rfifolock.h"
+
+void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque)
+{
+    qemu_mutex_init(&r->lock);
+    r->head = 0;
+    r->tail = 0;
+    qemu_cond_init(&r->cond);
+    r->nesting = 0;
+    r->cb = cb;
+    r->cb_opaque = opaque;
+}
+
+void rfifolock_destroy(RFifoLock *r)
+{
+    qemu_cond_destroy(&r->cond);
+    qemu_mutex_destroy(&r->lock);
+}
+
+/*
+ * Theory of operation:
+ *
+ * In order to ensure FIFO ordering, implement a ticketlock.  Threads acquiring
+ * the lock enqueue themselves by incrementing the tail index.  When the lock
+ * is unlocked, the head is incremented and waiting threads are notified.
+ *
+ * Recursive locking does not take a ticket since the head is only incremented
+ * when the outermost recursive caller unlocks.
+ */
+void rfifolock_lock(RFifoLock *r)
+{
+    qemu_mutex_lock(&r->lock);
+
+    /* Take a ticket */
+    unsigned int ticket = r->tail++;
+
+    if (r->nesting > 0 && qemu_thread_is_self(&r->owner_thread)) {
+        r->tail--; /* put ticket back, we're nesting */
+    } else {
+        while (ticket != r->head) {
+            /* Invoke optional contention callback */
+            if (r->cb) {
+                r->cb(r->cb_opaque);
+            }
+            qemu_cond_wait(&r->cond, &r->lock);
+        }
+    }
+
+    qemu_thread_get_self(&r->owner_thread);
+    r->nesting++;
+    qemu_mutex_unlock(&r->lock);
+}
+
+void rfifolock_unlock(RFifoLock *r)
+{
+    qemu_mutex_lock(&r->lock);
+    assert(r->nesting > 0);
+    assert(qemu_thread_is_self(&r->owner_thread));
+    if (--r->nesting == 0) {
+        r->head++;
+        qemu_cond_broadcast(&r->cond);
+    }
+    qemu_mutex_unlock(&r->lock);
+}
-- 
1.8.4.2

[Qemu-devel] [RFC v2 2/6] aio: add aio_context_acquire() and aio_context_release()

[Stefan Hajnoczi]

It can be useful to run an AioContext from a thread which normally does
not "own" the AioContext.  For example, request draining can be
implemented by acquiring the AioContext and looping aio_poll() until all
requests have been completed.

The following pattern should work:

  /* Event loop thread */
  while (running) {
      aio_context_acquire(ctx);
      aio_poll(ctx, true);
      aio_context_release(ctx);
  }

  /* Another thread */
  aio_context_acquire(ctx);
  bdrv_read(bs, 0x1000, buf, 1);
  aio_context_release(ctx);

This patch implements aio_context_acquire() and aio_context_release().

Note that existing aio_poll() callers do not need to worry about
acquiring and releasing - it is only needed when multiple threads will
call aio_poll() on the same AioContext.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 async.c             | 18 +++++++++++++++++
 include/block/aio.h | 18 +++++++++++++++++
 tests/test-aio.c    | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 94 insertions(+)

diff --git a/async.c b/async.c
index 5fb3fa6..6930185 100644
--- a/async.c
+++ b/async.c
@@ -214,6 +214,7 @@ aio_ctx_finalize(GSource     *source)
     thread_pool_free(ctx->thread_pool);
     aio_set_event_notifier(ctx, &ctx->notifier, NULL);
     event_notifier_cleanup(&ctx->notifier);
+    rfifolock_destroy(&ctx->lock);
     qemu_mutex_destroy(&ctx->bh_lock);
     g_array_free(ctx->pollfds, TRUE);
     timerlistgroup_deinit(&ctx->tlg);
@@ -250,6 +251,12 @@ static void aio_timerlist_notify(void *opaque)
     aio_notify(opaque);
 }
 
+static void aio_rfifolock_cb(void *opaque)
+{
+    /* Kick owner thread in case they are blocked in aio_poll() */
+    aio_notify(opaque);
+}
+
 AioContext *aio_context_new(void)
 {
     AioContext *ctx;
@@ -257,6 +264,7 @@ AioContext *aio_context_new(void)
     ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
     ctx->thread_pool = NULL;
     qemu_mutex_init(&ctx->bh_lock);
+    rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
     event_notifier_init(&ctx->notifier, false);
     aio_set_event_notifier(ctx, &ctx->notifier, 
                            (EventNotifierHandler *)
@@ -275,3 +283,13 @@ void aio_context_unref(AioContext *ctx)
 {
     g_source_unref(&ctx->source);
 }
+
+void aio_context_acquire(AioContext *ctx)
+{
+    rfifolock_lock(&ctx->lock);
+}
+
+void aio_context_release(AioContext *ctx)
+{
+    rfifolock_unlock(&ctx->lock);
+}
diff --git a/include/block/aio.h b/include/block/aio.h
index 2efdf41..4aaa5d5 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -19,6 +19,7 @@
 #include "qemu/queue.h"
 #include "qemu/event_notifier.h"
 #include "qemu/thread.h"
+#include "qemu/rfifolock.h"
 #include "qemu/timer.h"
 
 typedef struct BlockDriverAIOCB BlockDriverAIOCB;
@@ -47,6 +48,9 @@ typedef void IOHandler(void *opaque);
 struct AioContext {
     GSource source;
 
+    /* Protects all fields from multi-threaded access */
+    RFifoLock lock;
+
     /* The list of registered AIO handlers */
     QLIST_HEAD(, AioHandler) aio_handlers;
 
@@ -104,6 +108,20 @@ void aio_context_ref(AioContext *ctx);
  */
 void aio_context_unref(AioContext *ctx);
 
+/* Take ownership of the AioContext.  If the AioContext will be shared between
+ * threads, a thread must have ownership when calling aio_poll().
+ *
+ * Note that multiple threads calling aio_poll() means timers, BHs, and
+ * callbacks may be invoked from a different thread than they were registered
+ * from.  Therefore, code must use AioContext acquire/release or use
+ * fine-grained synchronization to protect shared state if other threads will
+ * be accessing it simultaneously.
+ */
+void aio_context_acquire(AioContext *ctx);
+
+/* Reliquinish ownership of the AioContext. */
+void aio_context_release(AioContext *ctx);
+
 /**
  * aio_bh_new: Allocate a new bottom half structure.
  *
diff --git a/tests/test-aio.c b/tests/test-aio.c
index 592721e..d384b0b 100644
--- a/tests/test-aio.c
+++ b/tests/test-aio.c
@@ -112,6 +112,63 @@ static void test_notify(void)
     g_assert(!aio_poll(ctx, false));
 }
 
+typedef struct {
+    QemuMutex start_lock;
+    bool thread_acquired;
+} AcquireTestData;
+
+static void *test_acquire_thread(void *opaque)
+{
+    AcquireTestData *data = opaque;
+
+    /* Wait for other thread to let us start */
+    qemu_mutex_lock(&data->start_lock);
+    qemu_mutex_unlock(&data->start_lock);
+
+    aio_context_acquire(ctx);
+    aio_context_release(ctx);
+
+    data->thread_acquired = true; /* success, we got here */
+
+    return NULL;
+}
+
+static void dummy_notifier_read(EventNotifier *unused)
+{
+    g_assert(false); /* should never be invoked */
+}
+
+static void test_acquire(void)
+{
+    QemuThread thread;
+    EventNotifier notifier;
+    AcquireTestData data;
+
+    /* Dummy event notifier ensures aio_poll() will block */
+    event_notifier_init(&notifier, false);
+    aio_set_event_notifier(ctx, &notifier, dummy_notifier_read);
+    g_assert(!aio_poll(ctx, false)); /* consume aio_notify() */
+
+    qemu_mutex_init(&data.start_lock);
+    qemu_mutex_lock(&data.start_lock);
+    data.thread_acquired = false;
+
+    qemu_thread_create(&thread, test_acquire_thread,
+                       &data, QEMU_THREAD_JOINABLE);
+
+    /* Block in aio_poll(), let other thread kick us and acquire context */
+    aio_context_acquire(ctx);
+    qemu_mutex_unlock(&data.start_lock); /* let the thread run */
+    g_assert(!aio_poll(ctx, true));
+    aio_context_release(ctx);
+
+    qemu_thread_join(&thread);
+    aio_set_event_notifier(ctx, &notifier, NULL);
+    event_notifier_cleanup(&notifier);
+
+    g_assert(data.thread_acquired);
+}
+
 static void test_bh_schedule(void)
 {
     BHTestData data = { .n = 0 };
@@ -775,6 +832,7 @@ int main(int argc, char **argv)
 
     g_test_init(&argc, &argv, NULL);
     g_test_add_func("/aio/notify",                  test_notify);
+    g_test_add_func("/aio/acquire",                 test_acquire);
     g_test_add_func("/aio/bh/schedule",             test_bh_schedule);
     g_test_add_func("/aio/bh/schedule10",           test_bh_schedule10);
     g_test_add_func("/aio/bh/cancel",               test_bh_cancel);
-- 
1.8.4.2

[Qemu-devel] [RFC v2 3/6] iothread: add I/O thread object

[Stefan Hajnoczi]

This is a stand-in for Michael Roth's QContext.  I expect this to be
replaced once QContext is completed.

The IOThread object is an AioContext event loop thread.  This patch adds
the concept of multiple event loop threads, allowing users to define
them.

When SMP guests run on SMP hosts it makes sense to instantiate multiple
IOThreads.  This spreads event loop processing across multiple cores.
Note that additional patches are required to actually bind a device to
an IOThread.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 Makefile.objs             |   1 +
 include/sysemu/iothread.h |  30 +++++++++++
 iothread.c                | 132 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 163 insertions(+)
 create mode 100644 include/sysemu/iothread.h
 create mode 100644 iothread.c

diff --git a/Makefile.objs b/Makefile.objs
index 2b6c1fe..a1102a5 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -42,6 +42,7 @@ libcacard-y += libcacard/vcardt.o
 
 ifeq ($(CONFIG_SOFTMMU),y)
 common-obj-y = $(block-obj-y) blockdev.o blockdev-nbd.o block/
+common-obj-y += iothread.o
 common-obj-y += net/
 common-obj-y += readline.o
 common-obj-y += qdev-monitor.o device-hotplug.o
diff --git a/include/sysemu/iothread.h b/include/sysemu/iothread.h
new file mode 100644
index 0000000..a32214a
--- /dev/null
+++ b/include/sysemu/iothread.h
@@ -0,0 +1,30 @@
+/*
+ * Event loop thread
+ *
+ * Copyright Red Hat Inc., 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <stefanha@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef IOTHREAD_H
+#define IOTHREAD_H
+
+#include "block/aio.h"
+
+#define TYPE_IOTHREAD "iothread"
+
+typedef struct IOThread IOThread;
+
+#define IOTHREAD(obj) \
+   OBJECT_CHECK(IOThread, obj, TYPE_IOTHREAD)
+
+IOThread *iothread_find(const char *id);
+char *iothread_get_id(IOThread *iothread);
+AioContext *iothread_get_aio_context(IOThread *iothread);
+
+#endif /* IOTHREAD_H */
diff --git a/iothread.c b/iothread.c
new file mode 100644
index 0000000..b925889
--- /dev/null
+++ b/iothread.c
@@ -0,0 +1,132 @@
+/*
+ * Event loop thread
+ *
+ * Copyright Red Hat Inc., 2013
+ *
+ * Authors:
+ *  Stefan Hajnoczi   <stefanha@redhat.com>
+ *
+ * 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 "qom/object.h"
+#include "qom/object_interfaces.h"
+#include "qemu/module.h"
+#include "qemu/thread.h"
+#include "block/aio.h"
+#include "sysemu/iothread.h"
+
+#define IOTHREADS_PATH "/backends/iothreads"
+
+typedef ObjectClass IOThreadClass;
+struct IOThread {
+    Object parent;
+    QemuThread thread;
+    AioContext *ctx;
+    bool stopping;
+};
+
+#define IOTHREAD_GET_CLASS(obj) \
+   OBJECT_GET_CLASS(IOThreadClass, obj, TYPE_IOTHREAD)
+#define IOTHREAD_CLASS(klass) \
+   OBJECT_CLASS_CHECK(IOThreadClass, klass, TYPE_IOTHREAD)
+
+static void *iothread_run(void *opaque)
+{
+    IOThread *iothread = opaque;
+
+    while (!iothread->stopping) {
+        aio_context_acquire(iothread->ctx);
+        while (!iothread->stopping && aio_poll(iothread->ctx, true)) {
+            /* Progress was made, keep going */
+        }
+        aio_context_release(iothread->ctx);
+    }
+    return NULL;
+}
+
+static void iothread_instance_finalize(Object *obj)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    iothread->stopping = true;
+    aio_notify(iothread->ctx);
+    qemu_thread_join(&iothread->thread);
+    aio_context_unref(iothread->ctx);
+}
+
+static void iothread_realize(ObjectRealizeInterface *obj, Error **errp)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    iothread->stopping = false;
+    iothread->ctx = aio_context_new();
+
+    /* This assumes we are called from a thread with useful CPU affinity for us
+     * to inherit.
+     */
+    qemu_thread_create(&iothread->thread, iothread_run,
+                       iothread, QEMU_THREAD_JOINABLE);
+}
+
+static const char *iothread_default_parent(ObjectPathInterface *obj)
+{
+    return IOTHREADS_PATH;
+}
+
+static void iothread_class_init(ObjectClass *klass, void *class_data)
+{
+    ObjectRealizeInterfaceClass *orc = OBJECT_REALIZE_INTERFACE_CLASS(klass);
+    orc->realize = iothread_realize;
+
+    ObjectPathInterfaceClass *opc = OBJECT_PATH_INTERFACE_CLASS(klass);
+    opc->default_parent = iothread_default_parent;
+}
+
+static const TypeInfo iothread_info = {
+    .name = TYPE_IOTHREAD,
+    .parent = TYPE_OBJECT,
+    .class_init = iothread_class_init,
+    .instance_size = sizeof(IOThread),
+    .instance_finalize = iothread_instance_finalize,
+    .interfaces = (InterfaceInfo[]) {
+        {TYPE_OBJECT_REALIZE_INTERFACE},
+        {TYPE_OBJECT_PATH_INTERFACE},
+        {}
+    },
+};
+
+static void iothread_register_types(void)
+{
+    type_register_static(&iothread_info);
+}
+
+type_init(iothread_register_types)
+
+IOThread *iothread_find(const char *id)
+{
+    Object *container = container_get(object_get_root(), IOTHREADS_PATH);
+    Object *child;
+
+    child = object_property_get_link(container, id, NULL);
+    if (!child) {
+        return NULL;
+    }
+    return IOTHREAD(child);
+}
+
+char *iothread_get_id(IOThread *iothread)
+{
+    /* The last path component is the identifier */
+    char *path = object_get_canonical_path(OBJECT(iothread));
+    char *id = g_strdup(&path[sizeof(IOTHREADS_PATH)]);
+    g_free(path);
+    return id;
+}
+
+AioContext *iothread_get_aio_context(IOThread *iothread)
+{
+    return iothread->ctx;
+}
-- 
1.8.4.2

[Qemu-devel] [RFC v2 4/6] qdev: add get_pointer_and_free() for temporary strings

[Stefan Hajnoczi]

get_pointer() assumes the string has unspecified lifetime (at least as
long as the object is alive).  In some cases we can only produce a
temporary string that should be freed when get_pointer() is done.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/core/qdev-properties-system.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 729efa8..200f853 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -31,6 +31,20 @@ static void get_pointer(Object *obj, Visitor *v, Property *prop,
     visit_type_str(v, &p, name, errp);
 }
 
+/* Same as get_pointer() but frees heap-allocated print() return value */
+static void get_pointer_and_free(Object *obj, Visitor *v, Property *prop,
+                                 char *(*print)(void *ptr),
+                                 const char *name, Error **errp)
+{
+    DeviceState *dev = DEVICE(obj);
+    void **ptr = qdev_get_prop_ptr(dev, prop);
+    char *p;
+
+    p = *ptr ? print(*ptr) : g_strdup("");
+    visit_type_str(v, &p, name, errp);
+    g_free(p);
+}
+
 static void set_pointer(Object *obj, Visitor *v, Property *prop,
                         int (*parse)(DeviceState *dev, const char *str,
                                      void **ptr),
-- 
1.8.4.2

[Qemu-devel] [RFC v2 5/6] iothread: add "iothread" qdev property type

[Stefan Hajnoczi]

Add a "iothread" qdev property type so devices can be hooked up to an
IOThread from the comand-line:

  qemu -object iothread,id=iothread0 \
       -device some-device,iothread=iothread0

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/core/qdev-properties-system.c | 51 ++++++++++++++++++++++++++++++++++++++++
 include/hw/qdev-properties.h     |  3 +++
 2 files changed, 54 insertions(+)

diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 200f853..95b63b6 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -18,6 +18,7 @@
 #include "net/hub.h"
 #include "qapi/visitor.h"
 #include "sysemu/char.h"
+#include "sysemu/iothread.h"
 
 static void get_pointer(Object *obj, Visitor *v, Property *prop,
                         const char *(*print)(void *ptr),
@@ -396,6 +397,56 @@ void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd)
     nd->instantiated = 1;
 }
 
+/* --- iothread --- */
+
+static char *print_iothread(void *ptr)
+{
+    return iothread_get_id(ptr);
+}
+
+static int parse_iothread(DeviceState *dev, const char *str, void **ptr)
+{
+    IOThread *iothread;
+
+    iothread = iothread_find(str);
+    if (!iothread) {
+        return -ENOENT;
+    }
+    object_ref(OBJECT(iothread));
+    *ptr = iothread;
+    return 0;
+}
+
+static void get_iothread(Object *obj, struct Visitor *v, void *opaque,
+                         const char *name, Error **errp)
+{
+    get_pointer_and_free(obj, v, opaque, print_iothread, name, errp);
+}
+
+static void set_iothread(Object *obj, struct Visitor *v, void *opaque,
+                         const char *name, Error **errp)
+{
+    set_pointer(obj, v, opaque, parse_iothread, name, errp);
+}
+
+static void release_iothread(Object *obj, const char *name, void *opaque)
+{
+    DeviceState *dev = DEVICE(obj);
+    Property *prop = opaque;
+    IOThread **ptr = qdev_get_prop_ptr(dev, prop);
+
+    if (*ptr) {
+        object_unref(OBJECT(*ptr));
+    }
+}
+
+PropertyInfo qdev_prop_iothread = {
+    .name = "iothread",
+    .get = get_iothread,
+    .set = set_iothread,
+    .release = release_iothread,
+};
+
 static int qdev_add_one_global(QemuOpts *opts, void *opaque)
 {
     GlobalProperty *g;
diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
index 692f82e..4048f9b 100644
--- a/include/hw/qdev-properties.h
+++ b/include/hw/qdev-properties.h
@@ -25,6 +25,7 @@ extern PropertyInfo qdev_prop_bios_chs_trans;
 extern PropertyInfo qdev_prop_drive;
 extern PropertyInfo qdev_prop_netdev;
 extern PropertyInfo qdev_prop_vlan;
+extern PropertyInfo qdev_prop_iothread;
 extern PropertyInfo qdev_prop_pci_devfn;
 extern PropertyInfo qdev_prop_blocksize;
 extern PropertyInfo qdev_prop_pci_host_devaddr;
@@ -134,6 +135,8 @@ extern PropertyInfo qdev_prop_arraylen;
     DEFINE_PROP(_n, _s, _f, qdev_prop_vlan, NICPeers)
 #define DEFINE_PROP_DRIVE(_n, _s, _f) \
     DEFINE_PROP(_n, _s, _f, qdev_prop_drive, BlockDriverState *)
+#define DEFINE_PROP_IOTHREAD(_n, _s, _f)             \
+    DEFINE_PROP(_n, _s, _f, qdev_prop_iothread, IOThread *)
 #define DEFINE_PROP_MACADDR(_n, _s, _f)         \
     DEFINE_PROP(_n, _s, _f, qdev_prop_macaddr, MACAddr)
 #define DEFINE_PROP_LOSTTICKPOLICY(_n, _s, _f, _d) \
-- 
1.8.4.2

[Qemu-devel] [RFC v2 6/6] dataplane: replace internal thread with IOThread

[Stefan Hajnoczi]

Today virtio-blk dataplane uses a 1:1 device-per-thread model.  Now that
IOThreads have been introduced we can generalize this to N:M devices per
threads.

This patch drops thread code from dataplane in favor of running inside
an IOThread AioContext.

As a bonus we solve the case where a guest keeps submitting I/O requests
while dataplane is trying to stop.  Previously the dataplane thread
would continue to process requests until the request gave it a break.
Now we can shut down in bounded time thanks to
aio_context_acquire/release.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 95 +++++++++++++++++++++++------------------
 include/hw/virtio/virtio-blk.h  |  8 +++-
 2 files changed, 59 insertions(+), 44 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 1e57f3a..6f30063 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -23,6 +23,7 @@
 #include "virtio-blk.h"
 #include "block/aio.h"
 #include "hw/virtio/virtio-bus.h"
+#include "monitor/monitor.h"
 
 enum {
     SEG_MAX = 126,                  /* maximum number of I/O segments */
@@ -44,8 +45,6 @@ struct VirtIOBlockDataPlane {
     bool started;
     bool starting;
     bool stopping;
-    QEMUBH *start_bh;
-    QemuThread thread;
 
     VirtIOBlkConf *blk;
     int fd;                         /* image file descriptor */
@@ -59,12 +58,14 @@ struct VirtIOBlockDataPlane {
      * (because you don't own the file descriptor or handle; you just
      * use it).
      */
+    IOThread *iothread;
+    bool internal_iothread;
     AioContext *ctx;
     EventNotifier io_notifier;      /* Linux AIO completion */
     EventNotifier host_notifier;    /* doorbell */
 
     IOQueue ioqueue;                /* Linux AIO queue (should really be per
-                                       dataplane thread) */
+                                       IOThread) */
     VirtIOBlockRequest requests[REQ_MAX]; /* pool of requests, managed by the
                                              queue */
 
@@ -360,26 +361,7 @@ static void handle_io(EventNotifier *e)
     }
 }
 
-static void *data_plane_thread(void *opaque)
-{
-    VirtIOBlockDataPlane *s = opaque;
-
-    while (!s->stopping || s->num_reqs > 0) {
-        aio_poll(s->ctx, true);
-    }
-    return NULL;
-}
-
-static void start_data_plane_bh(void *opaque)
-{
-    VirtIOBlockDataPlane *s = opaque;
-
-    qemu_bh_delete(s->start_bh);
-    s->start_bh = NULL;
-    qemu_thread_create(&s->thread, data_plane_thread,
-                       s, QEMU_THREAD_JOINABLE);
-}
-
+/* Context: QEMU global mutex held */
 void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
                                   VirtIOBlockDataPlane **dataplane,
                                   Error **errp)
@@ -426,12 +408,32 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
     s->fd = fd;
     s->blk = blk;
 
+    if (blk->iothread) {
+        s->internal_iothread = false;
+        s->iothread = blk->iothread;
+        object_ref(OBJECT(s->iothread));
+    } else {
+        /* Create per-device IOThread if none specified */
+        s->internal_iothread = true;
+        Error *local_err = NULL;
+        object_add(TYPE_IOTHREAD, vdev->name, NULL, NULL, &local_err);
+        if (error_is_set(&local_err)) {
+            error_propagate(errp, local_err);
+            g_free(s);
+            return;
+        }
+        s->iothread = iothread_find(vdev->name);
+        assert(s->iothread);
+    }
+    s->ctx = iothread_get_aio_context(s->iothread);
+
     /* Prevent block operations that conflict with data plane thread */
     bdrv_set_in_use(blk->conf.bs, 1);
 
     *dataplane = s;
 }
 
+/* Context: QEMU global mutex held */
 void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
 {
     if (!s) {
@@ -440,9 +442,14 @@ void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
 
     virtio_blk_data_plane_stop(s);
     bdrv_set_in_use(s->blk->conf.bs, 0);
+    object_unref(OBJECT(s->iothread));
+    if (s->internal_iothread) {
+        object_unparent(OBJECT(s->iothread));
+    }
     g_free(s);
 }
 
+/* Context: QEMU global mutex held */
 void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
 {
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s->vdev)));
@@ -466,8 +473,6 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
         return;
     }
 
-    s->ctx = aio_context_new();
-
     /* Set up guest notifier (irq) */
     if (k->set_guest_notifiers(qbus->parent, 1, true) != 0) {
         fprintf(stderr, "virtio-blk failed to set guest notifier, "
@@ -482,7 +487,6 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
         exit(1);
     }
     s->host_notifier = *virtio_queue_get_host_notifier(vq);
-    aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
 
     /* Set up ioqueue */
     ioq_init(&s->ioqueue, s->fd, REQ_MAX);
@@ -490,7 +494,6 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
         ioq_put_iocb(&s->ioqueue, &s->requests[i].iocb);
     }
     s->io_notifier = *ioq_get_notifier(&s->ioqueue);
-    aio_set_event_notifier(s->ctx, &s->io_notifier, handle_io);
 
     s->starting = false;
     s->started = true;
@@ -499,11 +502,14 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
     /* Kick right away to begin processing requests already in vring */
     event_notifier_set(virtio_queue_get_host_notifier(vq));
 
-    /* Spawn thread in BH so it inherits iothread cpusets */
-    s->start_bh = qemu_bh_new(start_data_plane_bh, s);
-    qemu_bh_schedule(s->start_bh);
+    /* Get this show started by hooking up our callbacks */
+    aio_context_acquire(s->ctx);
+    aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
+    aio_set_event_notifier(s->ctx, &s->io_notifier, handle_io);
+    aio_context_release(s->ctx);
 }
 
+/* Context: QEMU global mutex held */
 void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
 {
     BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(s->vdev)));
@@ -514,27 +520,32 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
     s->stopping = true;
     trace_virtio_blk_data_plane_stop(s);
 
-    /* Stop thread or cancel pending thread creation BH */
-    if (s->start_bh) {
-        qemu_bh_delete(s->start_bh);
-        s->start_bh = NULL;
-    } else {
-        aio_notify(s->ctx);
-        qemu_thread_join(&s->thread);
+    aio_context_acquire(s->ctx);
+
+    /* Stop notifications for new requests from guest */
+    aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);
+
+    /* Complete pending requests */
+    while (s->num_reqs > 0) {
+        aio_poll(s->ctx, true);
     }
 
+    /* Stop ioq callbacks (there are no pending requests left) */
     aio_set_event_notifier(s->ctx, &s->io_notifier, NULL);
-    ioq_cleanup(&s->ioqueue);
 
-    aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);
-    k->set_host_notifier(qbus->parent, 0, false);
+    aio_context_release(s->ctx);
 
-    aio_context_unref(s->ctx);
+    /* Sync vring state back to virtqueue so that non-dataplane request
+     * processing can continue when we disable the host notifier below.
+     */
+    vring_teardown(&s->vring, s->vdev, 0);
+
+    ioq_cleanup(&s->ioqueue);
+    k->set_host_notifier(qbus->parent, 0, false);
 
     /* Clean up guest notifier (irq) */
     k->set_guest_notifiers(qbus->parent, 1, false);
 
-    vring_teardown(&s->vring, s->vdev, 0);
     s->started = false;
     s->stopping = false;
 }
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 41885da..12193fd 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -16,6 +16,7 @@
 
 #include "hw/virtio/virtio.h"
 #include "hw/block/block.h"
+#include "sysemu/iothread.h"
 
 #define TYPE_VIRTIO_BLK "virtio-blk-device"
 #define VIRTIO_BLK(obj) \
@@ -106,6 +107,7 @@ struct virtio_scsi_inhdr
 struct VirtIOBlkConf
 {
     BlockConf conf;
+    IOThread *iothread;
     char *serial;
     uint32_t scsi;
     uint32_t config_wce;
@@ -140,13 +142,15 @@ typedef struct VirtIOBlock {
         DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf),                     \
         DEFINE_PROP_STRING("serial", _state, _field.serial),                  \
         DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true),    \
-        DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true)
+        DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true),                \
+        DEFINE_PROP_IOTHREAD("iothread", _state, _field.iothread)
 #else
 #define DEFINE_VIRTIO_BLK_PROPERTIES(_state, _field)                          \
         DEFINE_BLOCK_PROPERTIES(_state, _field.conf),                         \
         DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf),                     \
         DEFINE_PROP_STRING("serial", _state, _field.serial),                  \
-        DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true)
+        DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true),    \
+        DEFINE_PROP_IOTHREAD("iothread", _state, _field.iothread)
 #endif /* __linux__ */
 
 void virtio_blk_set_conf(DeviceState *dev, VirtIOBlkConf *blk);
-- 
1.8.4.2

Re: [Qemu-devel] [RFC v2 1/6] rfifolock: add recursive FIFO lock

[Fam Zheng]

On Fri, 01/10 09:45, Stefan Hajnoczi wrote:
> QemuMutex does not guarantee fairness and cannot be acquired
> recursively:
> 
> Fairness means each locker gets a turn and the scheduler cannot cause
> starvation.
> 
> Recursive locking is useful for composition, it allows a sequence of
> locking operations to be invoked atomically by acquiring the lock around
> them.
> 
> This patch adds RFifoLock, a recursive lock that guarantees FIFO order.
> Its first user is added in the next patch.
> 
> RFifoLock has one additional feature: it can be initialized with an
> optional contention callback.  The callback is invoked whenever a thread
> must wait for the lock.  For example, it can be used to poke the current
> owner so that they release the lock soon.
> 

Is it better to make the contention callback per-caller than per-lock?
Considering that different caller may want to do different things depending on
current code path.

Fam

> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  include/qemu/rfifolock.h | 54 +++++++++++++++++++++++++++++
>  tests/Makefile           |  2 ++
>  tests/test-rfifolock.c   | 90 ++++++++++++++++++++++++++++++++++++++++++++++++
>  util/Makefile.objs       |  1 +
>  util/rfifolock.c         | 78 +++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 225 insertions(+)
>  create mode 100644 include/qemu/rfifolock.h
>  create mode 100644 tests/test-rfifolock.c
>  create mode 100644 util/rfifolock.c
> 
> diff --git a/include/qemu/rfifolock.h b/include/qemu/rfifolock.h
> new file mode 100644
> index 0000000..b23ab53
> --- /dev/null
> +++ b/include/qemu/rfifolock.h
> @@ -0,0 +1,54 @@
> +/*
> + * Recursive FIFO lock
> + *
> + * Copyright Red Hat, Inc. 2013
> + *
> + * Authors:
> + *  Stefan Hajnoczi   <stefanha@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#ifndef QEMU_RFIFOLOCK_H
> +#define QEMU_RFIFOLOCK_H
> +
> +#include "qemu/thread.h"
> +
> +/* Recursive FIFO lock
> + *
> + * This lock provides more features than a plain mutex:
> + *
> + * 1. Fairness - enforces FIFO order.
> + * 2. Nesting - can be taken recursively.
> + * 3. Contention callback - optional, called when thread must wait.
> + *
> + * The recursive FIFO lock is heavyweight so prefer other synchronization
> + * primitives if you do not need its features.
> + */
> +typedef struct {
> +    QemuMutex lock;             /* protects all fields */
> +
> +    /* FIFO order */
> +    unsigned int head;          /* active ticket number */
> +    unsigned int tail;          /* waiting ticket number */
> +    QemuCond cond;              /* used to wait for our ticket number */
> +
> +    /* Nesting */
> +    QemuThread owner_thread;    /* thread that currently has ownership */
> +    unsigned int nesting;       /* amount of nesting levels */
> +
> +    /* Contention callback */
> +    void (*cb)(void *);         /* called when thread must wait, with ->lock
> +                                 * held so it may not recursively lock/unlock
> +                                 */
> +    void *cb_opaque;
> +} RFifoLock;
> +
> +void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque);
> +void rfifolock_destroy(RFifoLock *r);
> +void rfifolock_lock(RFifoLock *r);
> +void rfifolock_unlock(RFifoLock *r);
> +
> +#endif /* QEMU_RFIFOLOCK_H */
> diff --git a/tests/Makefile b/tests/Makefile
> index 0b85a34..b1b3686 100644
> --- a/tests/Makefile
> +++ b/tests/Makefile
> @@ -31,6 +31,7 @@ check-unit-y += tests/test-visitor-serialization$(EXESUF)
>  check-unit-y += tests/test-iov$(EXESUF)
>  gcov-files-test-iov-y = util/iov.c
>  check-unit-y += tests/test-aio$(EXESUF)
> +check-unit-y += tests/test-rfifolock$(EXESUF)
>  check-unit-y += tests/test-throttle$(EXESUF)
>  gcov-files-test-aio-$(CONFIG_WIN32) = aio-win32.c
>  gcov-files-test-aio-$(CONFIG_POSIX) = aio-posix.c
> @@ -153,6 +154,7 @@ tests/check-qjson$(EXESUF): tests/check-qjson.o libqemuutil.a libqemustub.a
>  tests/check-qom-interface$(EXESUF): tests/check-qom-interface.o $(qom-core-obj) libqemuutil.a
>  tests/test-coroutine$(EXESUF): tests/test-coroutine.o $(block-obj-y) libqemuutil.a libqemustub.a
>  tests/test-aio$(EXESUF): tests/test-aio.o $(block-obj-y) libqemuutil.a libqemustub.a
> +tests/test-rfifolock$(EXESUF): tests/test-rfifolock.o libqemuutil.a libqemustub.a
>  tests/test-throttle$(EXESUF): tests/test-throttle.o $(block-obj-y) libqemuutil.a libqemustub.a
>  tests/test-thread-pool$(EXESUF): tests/test-thread-pool.o $(block-obj-y) libqemuutil.a libqemustub.a
>  tests/test-iov$(EXESUF): tests/test-iov.o libqemuutil.a
> diff --git a/tests/test-rfifolock.c b/tests/test-rfifolock.c
> new file mode 100644
> index 0000000..440dbcb
> --- /dev/null
> +++ b/tests/test-rfifolock.c
> @@ -0,0 +1,90 @@
> +/*
> + * RFifoLock tests
> + *
> + * Copyright Red Hat, Inc. 2013
> + *
> + * Authors:
> + *  Stefan Hajnoczi    <stefanha@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2 or later.
> + * See the COPYING.LIB file in the top-level directory.
> + */
> +
> +#include <glib.h>
> +#include "qemu-common.h"
> +#include "qemu/rfifolock.h"
> +
> +static void test_nesting(void)
> +{
> +    RFifoLock lock;
> +
> +    /* Trivial test, ensure the lock is recursive */
> +    rfifolock_init(&lock, NULL, NULL);
> +    rfifolock_lock(&lock);
> +    rfifolock_lock(&lock);
> +    rfifolock_lock(&lock);
> +    rfifolock_unlock(&lock);
> +    rfifolock_unlock(&lock);
> +    rfifolock_unlock(&lock);
> +    rfifolock_destroy(&lock);
> +}
> +
> +typedef struct {
> +    RFifoLock lock;
> +    int fd[2];
> +} CallbackTestData;
> +
> +static void rfifolock_cb(void *opaque)
> +{
> +    CallbackTestData *data = opaque;
> +    int ret;
> +    char c = 0;
> +
> +    ret = write(data->fd[1], &c, sizeof(c));
> +    g_assert(ret == 1);
> +}
> +
> +static void *callback_thread(void *opaque)
> +{
> +    CallbackTestData *data = opaque;
> +
> +    /* The other thread holds the lock so the contention callback will be
> +     * invoked...
> +     */
> +    rfifolock_lock(&data->lock);
> +    rfifolock_unlock(&data->lock);
> +    return NULL;
> +}
> +
> +static void test_callback(void)
> +{
> +    CallbackTestData data;
> +    QemuThread thread;
> +    int ret;
> +    char c;
> +
> +    rfifolock_init(&data.lock, rfifolock_cb, &data);
> +    ret = qemu_pipe(data.fd);
> +    g_assert(ret == 0);
> +
> +    /* Hold lock but allow the callback to kick us by writing to the pipe */
> +    rfifolock_lock(&data.lock);
> +    qemu_thread_create(&thread, callback_thread, &data, QEMU_THREAD_JOINABLE);
> +    ret = read(data.fd[0], &c, sizeof(c));
> +    g_assert(ret == 1);
> +    rfifolock_unlock(&data.lock);
> +    /* If we got here then the callback was invoked, as expected */
> +
> +    qemu_thread_join(&thread);
> +    close(data.fd[0]);
> +    close(data.fd[1]);
> +    rfifolock_destroy(&data.lock);
> +}
> +
> +int main(int argc, char **argv)
> +{
> +    g_test_init(&argc, &argv, NULL);
> +    g_test_add_func("/nesting", test_nesting);
> +    g_test_add_func("/callback", test_callback);
> +    return g_test_run();
> +}
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index af3e5cb..53a4c5e 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -13,3 +13,4 @@ util-obj-y += hexdump.o
>  util-obj-y += crc32c.o
>  util-obj-y += throttle.o
>  util-obj-y += getauxval.o
> +util-obj-y += rfifolock.o
> diff --git a/util/rfifolock.c b/util/rfifolock.c
> new file mode 100644
> index 0000000..afbf748
> --- /dev/null
> +++ b/util/rfifolock.c
> @@ -0,0 +1,78 @@
> +/*
> + * Recursive FIFO lock
> + *
> + * Copyright Red Hat, Inc. 2013
> + *
> + * Authors:
> + *  Stefan Hajnoczi   <stefanha@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2 or later.
> + * See the COPYING.LIB file in the top-level directory.
> + *
> + */
> +
> +#include <assert.h>
> +#include "qemu/rfifolock.h"
> +
> +void rfifolock_init(RFifoLock *r, void (*cb)(void *), void *opaque)
> +{
> +    qemu_mutex_init(&r->lock);
> +    r->head = 0;
> +    r->tail = 0;
> +    qemu_cond_init(&r->cond);
> +    r->nesting = 0;
> +    r->cb = cb;
> +    r->cb_opaque = opaque;
> +}
> +
> +void rfifolock_destroy(RFifoLock *r)
> +{
> +    qemu_cond_destroy(&r->cond);
> +    qemu_mutex_destroy(&r->lock);
> +}
> +
> +/*
> + * Theory of operation:
> + *
> + * In order to ensure FIFO ordering, implement a ticketlock.  Threads acquiring
> + * the lock enqueue themselves by incrementing the tail index.  When the lock
> + * is unlocked, the head is incremented and waiting threads are notified.
> + *
> + * Recursive locking does not take a ticket since the head is only incremented
> + * when the outermost recursive caller unlocks.
> + */
> +void rfifolock_lock(RFifoLock *r)
> +{
> +    qemu_mutex_lock(&r->lock);
> +
> +    /* Take a ticket */
> +    unsigned int ticket = r->tail++;
> +
> +    if (r->nesting > 0 && qemu_thread_is_self(&r->owner_thread)) {
> +        r->tail--; /* put ticket back, we're nesting */
> +    } else {
> +        while (ticket != r->head) {
> +            /* Invoke optional contention callback */
> +            if (r->cb) {
> +                r->cb(r->cb_opaque);
> +            }
> +            qemu_cond_wait(&r->cond, &r->lock);
> +        }
> +    }
> +
> +    qemu_thread_get_self(&r->owner_thread);
> +    r->nesting++;
> +    qemu_mutex_unlock(&r->lock);
> +}
> +
> +void rfifolock_unlock(RFifoLock *r)
> +{
> +    qemu_mutex_lock(&r->lock);
> +    assert(r->nesting > 0);
> +    assert(qemu_thread_is_self(&r->owner_thread));
> +    if (--r->nesting == 0) {
> +        r->head++;
> +        qemu_cond_broadcast(&r->cond);
> +    }
> +    qemu_mutex_unlock(&r->lock);
> +}
> -- 
> 1.8.4.2
> 
> 

Re: [Qemu-devel] [RFC v2 2/6] aio: add aio_context_acquire() and aio_context_release()

[Fam Zheng]

On Fri, 01/10 09:45, Stefan Hajnoczi wrote:
> It can be useful to run an AioContext from a thread which normally does
> not "own" the AioContext.  For example, request draining can be
> implemented by acquiring the AioContext and looping aio_poll() until all
> requests have been completed.
> 
> The following pattern should work:
> 
>   /* Event loop thread */
>   while (running) {
>       aio_context_acquire(ctx);
>       aio_poll(ctx, true);
>       aio_context_release(ctx);
>   }
> 
>   /* Another thread */
>   aio_context_acquire(ctx);
>   bdrv_read(bs, 0x1000, buf, 1);
>   aio_context_release(ctx);
> 
> This patch implements aio_context_acquire() and aio_context_release().
> 
> Note that existing aio_poll() callers do not need to worry about
> acquiring and releasing - it is only needed when multiple threads will
> call aio_poll() on the same AioContext.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  async.c             | 18 +++++++++++++++++
>  include/block/aio.h | 18 +++++++++++++++++
>  tests/test-aio.c    | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 94 insertions(+)
> 
> diff --git a/async.c b/async.c
> index 5fb3fa6..6930185 100644
> --- a/async.c
> +++ b/async.c
> @@ -214,6 +214,7 @@ aio_ctx_finalize(GSource     *source)
>      thread_pool_free(ctx->thread_pool);
>      aio_set_event_notifier(ctx, &ctx->notifier, NULL);
>      event_notifier_cleanup(&ctx->notifier);
> +    rfifolock_destroy(&ctx->lock);
>      qemu_mutex_destroy(&ctx->bh_lock);
>      g_array_free(ctx->pollfds, TRUE);
>      timerlistgroup_deinit(&ctx->tlg);
> @@ -250,6 +251,12 @@ static void aio_timerlist_notify(void *opaque)
>      aio_notify(opaque);
>  }
>  
> +static void aio_rfifolock_cb(void *opaque)
> +{
> +    /* Kick owner thread in case they are blocked in aio_poll() */
> +    aio_notify(opaque);
> +}
> +
>  AioContext *aio_context_new(void)
>  {
>      AioContext *ctx;
> @@ -257,6 +264,7 @@ AioContext *aio_context_new(void)
>      ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
>      ctx->thread_pool = NULL;
>      qemu_mutex_init(&ctx->bh_lock);
> +    rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx);
>      event_notifier_init(&ctx->notifier, false);
>      aio_set_event_notifier(ctx, &ctx->notifier, 
>                             (EventNotifierHandler *)
> @@ -275,3 +283,13 @@ void aio_context_unref(AioContext *ctx)
>  {
>      g_source_unref(&ctx->source);
>  }
> +
> +void aio_context_acquire(AioContext *ctx)
> +{
> +    rfifolock_lock(&ctx->lock);
> +}
> +
> +void aio_context_release(AioContext *ctx)
> +{
> +    rfifolock_unlock(&ctx->lock);
> +}
> diff --git a/include/block/aio.h b/include/block/aio.h
> index 2efdf41..4aaa5d5 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -19,6 +19,7 @@
>  #include "qemu/queue.h"
>  #include "qemu/event_notifier.h"
>  #include "qemu/thread.h"
> +#include "qemu/rfifolock.h"
>  #include "qemu/timer.h"
>  
>  typedef struct BlockDriverAIOCB BlockDriverAIOCB;
> @@ -47,6 +48,9 @@ typedef void IOHandler(void *opaque);
>  struct AioContext {
>      GSource source;
>  
> +    /* Protects all fields from multi-threaded access */
> +    RFifoLock lock;
> +
>      /* The list of registered AIO handlers */
>      QLIST_HEAD(, AioHandler) aio_handlers;
>  
> @@ -104,6 +108,20 @@ void aio_context_ref(AioContext *ctx);
>   */
>  void aio_context_unref(AioContext *ctx);
>  
> +/* Take ownership of the AioContext.  If the AioContext will be shared between
> + * threads, a thread must have ownership when calling aio_poll().
> + *
> + * Note that multiple threads calling aio_poll() means timers, BHs, and
> + * callbacks may be invoked from a different thread than they were registered
> + * from.  Therefore, code must use AioContext acquire/release or use
> + * fine-grained synchronization to protect shared state if other threads will
> + * be accessing it simultaneously.
> + */
> +void aio_context_acquire(AioContext *ctx);
> +
> +/* Reliquinish ownership of the AioContext. */

s/Reliquinish/Relinquish/

Fam

> +void aio_context_release(AioContext *ctx);
> +
>  /**
>   * aio_bh_new: Allocate a new bottom half structure.
>   *
> diff --git a/tests/test-aio.c b/tests/test-aio.c
> index 592721e..d384b0b 100644
> --- a/tests/test-aio.c
> +++ b/tests/test-aio.c
> @@ -112,6 +112,63 @@ static void test_notify(void)
>      g_assert(!aio_poll(ctx, false));
>  }
>  
> +typedef struct {
> +    QemuMutex start_lock;
> +    bool thread_acquired;
> +} AcquireTestData;
> +
> +static void *test_acquire_thread(void *opaque)
> +{
> +    AcquireTestData *data = opaque;
> +
> +    /* Wait for other thread to let us start */
> +    qemu_mutex_lock(&data->start_lock);
> +    qemu_mutex_unlock(&data->start_lock);
> +
> +    aio_context_acquire(ctx);
> +    aio_context_release(ctx);
> +
> +    data->thread_acquired = true; /* success, we got here */
> +
> +    return NULL;
> +}
> +
> +static void dummy_notifier_read(EventNotifier *unused)
> +{
> +    g_assert(false); /* should never be invoked */
> +}
> +
> +static void test_acquire(void)
> +{
> +    QemuThread thread;
> +    EventNotifier notifier;
> +    AcquireTestData data;
> +
> +    /* Dummy event notifier ensures aio_poll() will block */
> +    event_notifier_init(&notifier, false);
> +    aio_set_event_notifier(ctx, &notifier, dummy_notifier_read);
> +    g_assert(!aio_poll(ctx, false)); /* consume aio_notify() */
> +
> +    qemu_mutex_init(&data.start_lock);
> +    qemu_mutex_lock(&data.start_lock);
> +    data.thread_acquired = false;
> +
> +    qemu_thread_create(&thread, test_acquire_thread,
> +                       &data, QEMU_THREAD_JOINABLE);
> +
> +    /* Block in aio_poll(), let other thread kick us and acquire context */
> +    aio_context_acquire(ctx);
> +    qemu_mutex_unlock(&data.start_lock); /* let the thread run */
> +    g_assert(!aio_poll(ctx, true));
> +    aio_context_release(ctx);
> +
> +    qemu_thread_join(&thread);
> +    aio_set_event_notifier(ctx, &notifier, NULL);
> +    event_notifier_cleanup(&notifier);
> +
> +    g_assert(data.thread_acquired);
> +}
> +
>  static void test_bh_schedule(void)
>  {
>      BHTestData data = { .n = 0 };
> @@ -775,6 +832,7 @@ int main(int argc, char **argv)
>  
>      g_test_init(&argc, &argv, NULL);
>      g_test_add_func("/aio/notify",                  test_notify);
> +    g_test_add_func("/aio/acquire",                 test_acquire);
>      g_test_add_func("/aio/bh/schedule",             test_bh_schedule);
>      g_test_add_func("/aio/bh/schedule10",           test_bh_schedule10);
>      g_test_add_func("/aio/bh/cancel",               test_bh_cancel);
> -- 
> 1.8.4.2
> 
> 

Re: [Qemu-devel] [RFC v2 1/6] rfifolock: add recursive FIFO lock

[Stefan Hajnoczi]

On Mon, Jan 20, 2014 at 06:22:28PM +0800, Fam Zheng wrote:
> On Fri, 01/10 09:45, Stefan Hajnoczi wrote:
> > QemuMutex does not guarantee fairness and cannot be acquired
> > recursively:
> > 
> > Fairness means each locker gets a turn and the scheduler cannot cause
> > starvation.
> > 
> > Recursive locking is useful for composition, it allows a sequence of
> > locking operations to be invoked atomically by acquiring the lock around
> > them.
> > 
> > This patch adds RFifoLock, a recursive lock that guarantees FIFO order.
> > Its first user is added in the next patch.
> > 
> > RFifoLock has one additional feature: it can be initialized with an
> > optional contention callback.  The callback is invoked whenever a thread
> > must wait for the lock.  For example, it can be used to poke the current
> > owner so that they release the lock soon.
> > 
> 
> Is it better to make the contention callback per-caller than per-lock?
> Considering that different caller may want to do different things depending on
> current code path.

Perhaps it will make sense to change it in the future.  For now it means
callers use the standard lock/unlock function.  They don't have to know
what actions are needed to poke the current lock-holder.

Re: [Qemu-devel] [RFC v2 2/6] aio: add aio_context_acquire() and aio_context_release()

[Stefan Hajnoczi]

On Mon, Jan 20, 2014 at 06:29:50PM +0800, Fam Zheng wrote:
> On Fri, 01/10 09:45, Stefan Hajnoczi wrote:
> > +/* Take ownership of the AioContext.  If the AioContext will be shared between
> > + * threads, a thread must have ownership when calling aio_poll().
> > + *
> > + * Note that multiple threads calling aio_poll() means timers, BHs, and
> > + * callbacks may be invoked from a different thread than they were registered
> > + * from.  Therefore, code must use AioContext acquire/release or use
> > + * fine-grained synchronization to protect shared state if other threads will
> > + * be accessing it simultaneously.
> > + */
> > +void aio_context_acquire(AioContext *ctx);
> > +
> > +/* Reliquinish ownership of the AioContext. */
> 
> s/Reliquinish/Relinquish/

Fixed in next version.