Re: [Qemu-devel] [PATCH 04/11] aio: introduce aio_co_schedule

[Fam Zheng]

On Fri, 04/15 13:31, Paolo Bonzini wrote:
> This provides the infrastructure to start a coroutine on a remote
> 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.
> 
> aio_co_schedule is based on a lock-free multiple-producer,
> single-consumer queue.  The multiple producers use cmpxchg to add
> to a LIFO stacks.  The consumer (a per-AioContext bottom half) grabs

s/stacks/stack/ ?

> all items added so far, inverts the list to make it FIFO, and goes
> through it one item at a time.
> 
> Most of the changes really are in infrastructure and tests.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  async.c                      |  38 ++++++++
>  include/block/aio.h          |   9 ++
>  include/qemu/coroutine_int.h |  10 +-
>  tests/Makefile               |  11 ++-
>  tests/iothread.c             |  91 ++++++++++++++++++
>  tests/iothread.h             |  25 +++++
>  tests/test-aio-multithread.c | 220 
> +++++++++++++++++++++++++++++++++++++++++++
>  trace-events                 |   4 +
>  8 files changed, 404 insertions(+), 4 deletions(-)
>  create mode 100644 tests/iothread.c
>  create mode 100644 tests/iothread.h
>  create mode 100644 tests/test-aio-multithread.c
> 
> diff --git a/async.c b/async.c
> index acd3627..ef8b409 100644
> --- a/async.c
> +++ b/async.c
> @@ -30,6 +30,8 @@
>  #include "qemu/main-loop.h"
>  #include "qemu/atomic.h"
>  #include "block/raw-aio.h"
> +#include "trace/generated-tracers.h"
> +#include "qemu/coroutine_int.h"
>  
>  /***********************************************************/
>  /* bottom halves (can be seen as timers which expire ASAP) */
> @@ -255,6 +257,8 @@ aio_ctx_finalize(GSource     *source)
>      }
>  #endif
>  
> +    qemu_bh_delete(ctx->schedule_bh);
> +
>      qemu_lockcnt_lock(&ctx->list_lock);
>      assert(!qemu_lockcnt_count(&ctx->list_lock));
>      while (ctx->first_bh) {
> @@ -335,6 +339,28 @@ static void event_notifier_dummy_cb(EventNotifier *e)
>  {
>  }
>  
> +static void schedule_bh_cb(void *opaque)
> +{
> +    AioContext *ctx = opaque;
> +    QSLIST_HEAD(, Coroutine) straight, reversed;
> +
> +    QSLIST_MOVE_ATOMIC(&reversed, &ctx->scheduled_coroutines);
> +    QSLIST_INIT(&straight);
> +
> +    while (!QSLIST_EMPTY(&reversed)) {
> +        Coroutine *co = QSLIST_FIRST(&reversed);
> +        QSLIST_REMOVE_HEAD(&reversed, co_scheduled_next);
> +        QSLIST_INSERT_HEAD(&straight, co, co_scheduled_next);
> +    }
> +
> +    while (!QSLIST_EMPTY(&straight)) {
> +        Coroutine *co = QSLIST_FIRST(&straight);
> +        QSLIST_REMOVE_HEAD(&straight, co_scheduled_next);
> +        trace_aio_schedule_bh_cb(ctx, co);
> +        qemu_coroutine_enter(co, NULL);
> +    }
> +}
> +
>  AioContext *aio_context_new(Error **errp)
>  {
>      int ret;
> diff --git a/include/block/aio.h b/include/block/aio.h
> index 8f55d1a..0a344c3 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -46,6 +46,7 @@ typedef struct AioHandler AioHandler;
>  typedef void QEMUBHFunc(void *opaque);
>  typedef void IOHandler(void *opaque);
>  
> +struct Coroutine;
>  struct ThreadPool;
>  struct LinuxAioState;
>  
> @@ -107,6 +108,9 @@ struct AioContext {
>      bool notified;
>      EventNotifier notifier;
>  
> +    QSLIST_HEAD(, Coroutine) scheduled_coroutines;
> +    QEMUBH *schedule_bh;

Maybe rename it to co_schedule_bh to reflect it's used for schedule coroutines?

> +
>      /* Thread pool for performing work and receiving completion callbacks.
>       * Has its own locking.
>       */

> +int main(int argc, char **argv)
> +{
> +    init_clocks();
> +
> +    g_test_init(&argc, &argv, NULL);
> +    g_test_add_func("/aio/multi/lifecycle", test_lifecycle);
> +    if (g_test_quick()) {
> +        g_test_add_func("/aio/multi/schedule", test_multi_co_schedule_1);
> +    } else {
> +        g_test_add_func("/aio/multi/schedule", test_multi_co_schedule_10);

Should they use different path names, like /aio/multi/schedule/{1,10}?

> +    }
> +    return g_test_run();
> +}

Fam