Re: [Qemu-devel] [PATCH v4 06/10] coroutine: add co_aio_sleep_ns() to allow sleep in block drivers

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Jul 26, 2013 at 03:10:48PM +0900, MORITA Kazutaka wrote:
> This helper function behaves similarly to co_sleep_ns(), but the
> sleeping coroutine will be resumed when using qemu_aio_wait().
> 
> Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
> ---
>  include/block/coroutine.h |  8 ++++++++
>  qemu-coroutine-sleep.c    | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 55 insertions(+)
> 
> diff --git a/include/block/coroutine.h b/include/block/coroutine.h
> index 377805a..23ea6e9 100644
> --- a/include/block/coroutine.h
> +++ b/include/block/coroutine.h
> @@ -210,6 +210,14 @@ void qemu_co_rwlock_unlock(CoRwlock *lock);
>  void coroutine_fn co_sleep_ns(QEMUClock *clock, int64_t ns);
>  
>  /**
> + * Yield the coroutine for a given duration
> + *
> + * Behaves similarly to co_sleep_ns(), but the sleeping coroutine will be
> + * resumed when using qemu_aio_wait().
> + */
> +void coroutine_fn co_aio_sleep_ns(int64_t ns);
> +
> +/**
>   * Yield until a file descriptor becomes readable
>   *
>   * Note that this function clobbers the handlers for the file descriptor.
> diff --git a/qemu-coroutine-sleep.c b/qemu-coroutine-sleep.c
> index 169ce5c..3955347 100644
> --- a/qemu-coroutine-sleep.c
> +++ b/qemu-coroutine-sleep.c
> @@ -13,6 +13,7 @@
>  
>  #include "block/coroutine.h"
>  #include "qemu/timer.h"
> +#include "qemu/thread.h"
>  
>  typedef struct CoSleepCB {
>      QEMUTimer *ts;
> @@ -37,3 +38,49 @@ void coroutine_fn co_sleep_ns(QEMUClock *clock, int64_t ns)
>      qemu_del_timer(sleep_cb.ts);
>      qemu_free_timer(sleep_cb.ts);
>  }
> +
> +typedef struct CoAioSleepCB {
> +    QEMUBH *bh;
> +    int64_t ns;
> +    Coroutine *co;
> +} CoAioSleepCB;
> +
> +static void co_aio_sleep_cb(void *opaque)
> +{
> +    CoAioSleepCB *aio_sleep_cb = opaque;
> +
> +    qemu_coroutine_enter(aio_sleep_cb->co, NULL);
> +}
> +
> +static void *sleep_thread(void *opaque)
> +{
> +    CoAioSleepCB *aio_sleep_cb = opaque;
> +    struct timespec req = {
> +        .tv_sec = aio_sleep_cb->ns / 1000000000,
> +        .tv_nsec = aio_sleep_cb->ns % 1000000000,
> +    };
> +    struct timespec rem;
> +
> +    while (nanosleep(&req, &rem) < 0 && errno == EINTR) {

This breaks the Windows build and makes qemu_aio_wait() spin instead of
blocking (wastes CPU).

I think Alex Bligh and Ping Fan's QEMUTimer in AioContext work is needed
here.  I have CCed them.  Their patches would allow you to use
co_sleep_ns() in qemu_aio_wait().

> +        req = rem;
> +    }
> +
> +    qemu_bh_schedule(aio_sleep_cb->bh);
> +
> +    return NULL;
> +}
> +
> +void coroutine_fn co_aio_sleep_ns(int64_t ns)
> +{
> +    CoAioSleepCB aio_sleep_cb = {
> +        .ns = ns,
> +        .co = qemu_coroutine_self(),
> +    };
> +    QemuThread thread;
> +
> +    aio_sleep_cb.bh = qemu_bh_new(co_aio_sleep_cb, &aio_sleep_cb);
> +    qemu_thread_create(&thread, sleep_thread, &aio_sleep_cb,
> +                       QEMU_THREAD_DETACHED);
> +    qemu_coroutine_yield();
> +    qemu_bh_delete(aio_sleep_cb.bh);
> +}
> -- 
> 1.8.1.3.566.gaa39828
> 
>