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aio: introduce aio_co_schedule and aio_co_wake

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aio_co_wake provides the infrastructure to start a coroutine on a "home"
AioContext.  It will be used by CoMutex and CoQueue, so that coroutines
don't jump from one context to another when they go to sleep on a
mutex or waitqueue.  However, it can also be used as a more efficient
alternative to one-shot bottom halves, and saves the effort of tracking
which AioContext a coroutine is running on.

aio_co_schedule is the part of aio_co_wake that starts a coroutine
on a remove AioContext, but it is also useful to implement e.g.
bdrv_set_aio_context callbacks.

The implementation of aio_co_schedule is based on a lock-free
multiple-producer, single-consumer queue.  The multiple producers use
cmpxchg to add to a LIFO stack.  The consumer (a per-AioContext bottom
half) grabs all items added so far, inverts the list to make it FIFO,
and goes through it one item at a time until it's empty.  The data
structure was inspired by OSv, which uses it in the very code we'll
"port" to QEMU for the thread-safe CoMutex.

Most of the new code is really tests.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170213135235.12274-3-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Paolo Bonzini 2017-02-13 14:52:19 +01:00 • committed by Stefan Hajnoczi
parent c2b38b277a
commit 0c330a734b
9 changed files with 453 additions and 4 deletions
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11
include/qemu/coroutine_int.h
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@ -40,12 +40,21 @@ struct Coroutine {
CoroutineEntry *entry;
void *entry_arg;
Coroutine *caller;
/* Only used when the coroutine has terminated. */
QSLIST_ENTRY(Coroutine) pool_next;
size_t locks_held;
/* Coroutines that should be woken up when we yield or terminate */
/* Coroutines that should be woken up when we yield or terminate.
* Only used when the coroutine is running.
*/
QSIMPLEQ_HEAD(, Coroutine) co_queue_wakeup;
/* Only used when the coroutine has yielded. */
AioContext *ctx;
QSIMPLEQ_ENTRY(Coroutine) co_queue_next;
QSLIST_ENTRY(Coroutine) co_scheduled_next;
};
Coroutine *qemu_coroutine_new(void);