aboutsummaryrefslogtreecommitdiff
path: root/include/block/aio.h
diff options
context:
space:
mode:
authorPaolo Bonzini <pbonzini@redhat.com>2020-04-07 10:07:45 -0400
committerStefan Hajnoczi <stefanha@redhat.com>2020-04-09 16:16:28 +0100
commit3c18a92dc4b55ca8cc37a755ed119f11c0f34099 (patch)
tree1153ea1812c170bcc50e72820bae2d585827c0a0 /include/block/aio.h
parent636b836d5f4e36ceebb788e2e0d4724f7f9406e1 (diff)
downloadqemu-arm-3c18a92dc4b55ca8cc37a755ed119f11c0f34099.tar.gz
aio-wait: delegate polling of main AioContext if BQL not held
Any thread that is not a iothread returns NULL for qemu_get_current_aio_context(). As a result, it would also return true for in_aio_context_home_thread(qemu_get_aio_context()), causing AIO_WAIT_WHILE to invoke aio_poll() directly. This is incorrect if the BQL is not held, because aio_poll() does not expect to run concurrently from multiple threads, and it can actually happen when savevm writes to the vmstate file from the migration thread. Therefore, restrict in_aio_context_home_thread to return true for the main AioContext only if the BQL is held. The function is moved to aio-wait.h because it is mostly used there and to avoid a circular reference between main-loop.h and block/aio.h. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20200407140746.8041-5-pbonzini@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'include/block/aio.h')
-rw-r--r--include/block/aio.h29
1 files changed, 10 insertions, 19 deletions
diff --git a/include/block/aio.h b/include/block/aio.h
index cb1989105a..62ed954344 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -133,12 +133,16 @@ struct AioContext {
AioHandlerList deleted_aio_handlers;
/* Used to avoid unnecessary event_notifier_set calls in aio_notify;
- * accessed with atomic primitives. If this field is 0, everything
- * (file descriptors, bottom halves, timers) will be re-evaluated
- * before the next blocking poll(), thus the event_notifier_set call
- * can be skipped. If it is non-zero, you may need to wake up a
- * concurrent aio_poll or the glib main event loop, making
- * event_notifier_set necessary.
+ * only written from the AioContext home thread, or under the BQL in
+ * the case of the main AioContext. However, it is read from any
+ * thread so it is still accessed with atomic primitives.
+ *
+ * If this field is 0, everything (file descriptors, bottom halves,
+ * timers) will be re-evaluated before the next blocking poll() or
+ * io_uring wait; therefore, the event_notifier_set call can be
+ * skipped. If it is non-zero, you may need to wake up a concurrent
+ * aio_poll or the glib main event loop, making event_notifier_set
+ * necessary.
*
* Bit 0 is reserved for GSource usage of the AioContext, and is 1
* between a call to aio_ctx_prepare and the next call to aio_ctx_check.
@@ -682,19 +686,6 @@ void aio_co_enter(AioContext *ctx, struct Coroutine *co);
AioContext *qemu_get_current_aio_context(void);
/**
- * in_aio_context_home_thread:
- * @ctx: the aio context
- *
- * Return whether we are running in the thread that normally runs @ctx. Note
- * that acquiring/releasing ctx does not affect the outcome, each AioContext
- * still only has one home thread that is responsible for running it.
- */
-static inline bool in_aio_context_home_thread(AioContext *ctx)
-{
- return ctx == qemu_get_current_aio_context();
-}
-
-/**
* aio_context_setup:
* @ctx: the aio context
*