Rename "QEMU global mutex" to "BQL" in comments and docs
The term "QEMU global mutex" is identical to the more widely used Big
QEMU Lock ("BQL"). Update the code comments and documentation to use
"BQL" instead of "QEMU global mutex".
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
Message-id: 20240102153529.486531-6-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/docs/devel/multi-thread-tcg.rst b/docs/devel/multi-thread-tcg.rst
index c9541a7..7302c3b 100644
--- a/docs/devel/multi-thread-tcg.rst
+++ b/docs/devel/multi-thread-tcg.rst
@@ -226,10 +226,9 @@
Emulated hardware state
-----------------------
-Currently thanks to KVM work any access to IO memory is automatically
-protected by the global iothread mutex, also known as the BQL (Big
-QEMU Lock). Any IO region that doesn't use global mutex is expected to
-do its own locking.
+Currently thanks to KVM work any access to IO memory is automatically protected
+by the BQL (Big QEMU Lock). Any IO region that doesn't use the BQL is expected
+to do its own locking.
However IO memory isn't the only way emulated hardware state can be
modified. Some architectures have model specific registers that
diff --git a/docs/devel/multiple-iothreads.txt b/docs/devel/multiple-iothreads.txt
index 4865196..de85767 100644
--- a/docs/devel/multiple-iothreads.txt
+++ b/docs/devel/multiple-iothreads.txt
@@ -5,7 +5,7 @@
This document explains the IOThread feature and how to write code that runs
-outside the QEMU global mutex.
+outside the BQL.
The main loop and IOThreads
---------------------------
@@ -29,13 +29,13 @@
several IOThreads instead of just one main loop. When set up correctly this
can improve I/O latency and reduce jitter seen by the guest.
-The main loop is also deeply associated with the QEMU global mutex, which is a
-scalability bottleneck in itself. vCPU threads and the main loop use the QEMU
-global mutex to serialize execution of QEMU code. This mutex is necessary
-because a lot of QEMU's code historically was not thread-safe.
+The main loop is also deeply associated with the BQL, which is a
+scalability bottleneck in itself. vCPU threads and the main loop use the BQL
+to serialize execution of QEMU code. This mutex is necessary because a lot of
+QEMU's code historically was not thread-safe.
The fact that all I/O processing is done in a single main loop and that the
-QEMU global mutex is contended by all vCPU threads and the main loop explain
+BQL is contended by all vCPU threads and the main loop explain
why it is desirable to place work into IOThreads.
The experimental virtio-blk data-plane implementation has been benchmarked and
@@ -66,7 +66,7 @@
Since they implicitly work on the main loop they cannot be used in code that
runs in an IOThread. They might cause a crash or deadlock if called from an
-IOThread since the QEMU global mutex is not held.
+IOThread since the BQL is not held.
Instead, use the AioContext functions directly (see include/block/aio.h):
* aio_set_fd_handler() - monitor a file descriptor
diff --git a/docs/devel/qapi-code-gen.rst b/docs/devel/qapi-code-gen.rst
index 7f78183..ea82285 100644
--- a/docs/devel/qapi-code-gen.rst
+++ b/docs/devel/qapi-code-gen.rst
@@ -594,7 +594,7 @@
Coroutine safety can be hard to prove, similar to thread safety. Common
pitfalls are:
-- The global mutex isn't held across ``qemu_coroutine_yield()``, so
+- The BQL isn't held across ``qemu_coroutine_yield()``, so
operations that used to assume that they execute atomically may have
to be more careful to protect against changes in the global state.
diff --git a/docs/devel/replay.rst b/docs/devel/replay.rst
index 0244be8..effd856 100644
--- a/docs/devel/replay.rst
+++ b/docs/devel/replay.rst
@@ -184,7 +184,7 @@
Reading and writing requests are created by CPU thread of QEMU. Later these
requests proceed to block layer which creates "bottom halves". Bottom
halves consist of callback and its parameters. They are processed when
-main loop locks the global mutex. These locks are not synchronized with
+main loop locks the BQL. These locks are not synchronized with
replaying process because main loop also processes the events that do not
affect the virtual machine state (like user interaction with monitor).
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 97a302c..ba22732 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -84,7 +84,7 @@
}
}
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
VirtIOBlockDataPlane **dataplane,
Error **errp)
@@ -148,7 +148,7 @@
return true;
}
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
{
VirtIOBlock *vblk;
@@ -179,7 +179,7 @@
g_free(s);
}
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
int virtio_blk_data_plane_start(VirtIODevice *vdev)
{
VirtIOBlock *vblk = VIRTIO_BLK(vdev);
@@ -310,7 +310,7 @@
virtio_queue_host_notifier_read(host_notifier);
}
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
void virtio_blk_data_plane_stop(VirtIODevice *vdev)
{
VirtIOBlock *vblk = VIRTIO_BLK(vdev);
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 315b7b3..b7a344c 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -1539,7 +1539,7 @@
VirtIODevice *vdev = VIRTIO_DEVICE(opaque);
/*
- * virtio_notify_config() needs to acquire the global mutex,
+ * virtio_notify_config() needs to acquire the BQL,
* so it can't be called from an iothread. Instead, schedule
* it to be run in the main context BH.
*/
diff --git a/hw/scsi/virtio-scsi-dataplane.c b/hw/scsi/virtio-scsi-dataplane.c
index 135e23f..2806a12 100644
--- a/hw/scsi/virtio-scsi-dataplane.c
+++ b/hw/scsi/virtio-scsi-dataplane.c
@@ -20,7 +20,7 @@
#include "scsi/constants.h"
#include "hw/virtio/virtio-bus.h"
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
void virtio_scsi_dataplane_setup(VirtIOSCSI *s, Error **errp)
{
VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s);
@@ -93,7 +93,7 @@
}
}
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
int virtio_scsi_dataplane_start(VirtIODevice *vdev)
{
int i;
@@ -185,7 +185,7 @@
return -ENOSYS;
}
-/* Context: QEMU global mutex held */
+/* Context: BQL held */
void virtio_scsi_dataplane_stop(VirtIODevice *vdev)
{
BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
diff --git a/include/block/blockjob.h b/include/block/blockjob.h
index e594c10..7061ab7 100644
--- a/include/block/blockjob.h
+++ b/include/block/blockjob.h
@@ -54,7 +54,7 @@
/**
* Speed that was set with @block_job_set_speed.
- * Always modified and read under QEMU global mutex (GLOBAL_STATE_CODE).
+ * Always modified and read under the BQL (GLOBAL_STATE_CODE).
*/
int64_t speed;
@@ -66,7 +66,7 @@
/**
* Block other operations when block job is running.
- * Always modified and read under QEMU global mutex (GLOBAL_STATE_CODE).
+ * Always modified and read under the BQL (GLOBAL_STATE_CODE).
*/
Error *blocker;
@@ -89,7 +89,7 @@
/**
* BlockDriverStates that are involved in this block job.
- * Always modified and read under QEMU global mutex (GLOBAL_STATE_CODE).
+ * Always modified and read under the BQL (GLOBAL_STATE_CODE).
*/
GSList *nodes;
} BlockJob;
diff --git a/include/io/task.h b/include/io/task.h
index dc7d32e..0b5342e 100644
--- a/include/io/task.h
+++ b/include/io/task.h
@@ -149,7 +149,7 @@
* lookups) to be easily run non-blocking. Reporting the
* results in the main thread context means that the caller
* typically does not need to be concerned about thread
- * safety wrt the QEMU global mutex.
+ * safety wrt the BQL.
*
* For example, the socket_listen() method will block the caller
* while DNS lookups take place if given a name, instead of IP
diff --git a/include/qemu/coroutine-core.h b/include/qemu/coroutine-core.h
index 230bb56..503bad6 100644
--- a/include/qemu/coroutine-core.h
+++ b/include/qemu/coroutine-core.h
@@ -22,7 +22,7 @@
* rather than callbacks, for operations that need to give up control while
* waiting for events to complete.
*
- * These functions are re-entrant and may be used outside the global mutex.
+ * These functions are re-entrant and may be used outside the BQL.
*
* Functions that execute in coroutine context cannot be called
* directly from normal functions. Use @coroutine_fn to mark such
diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index a65be66..e6aff45 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -26,7 +26,7 @@
* rather than callbacks, for operations that need to give up control while
* waiting for events to complete.
*
- * These functions are re-entrant and may be used outside the global mutex.
+ * These functions are re-entrant and may be used outside the BQL.
*
* Functions that execute in coroutine context cannot be called
* directly from normal functions. Use @coroutine_fn to mark such
diff --git a/net/tap.c b/net/tap.c
index c23d032..c698b70 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -219,7 +219,7 @@
/*
* When the host keeps receiving more packets while tap_send() is
- * running we can hog the QEMU global mutex. Limit the number of
+ * running we can hog the BQL. Limit the number of
* packets that are processed per tap_send() callback to prevent
* stalling the guest.
*/
