Re: [Qemu-devel] [PATCH 2/2] aio: make aio_poll(ctx, true) block with no fds

[Alex Bligh]

On 25 Sep 2013, at 13:15, Stefan Hajnoczi wrote:

> This patch drops a special case where aio_poll(ctx, true) returns false
> instead of blocking if no file descriptors are waiting on I/O.  Now it
> is possible to block in aio_poll() to wait for aio_notify().
> 
> This change eliminates busy waiting.  bdrv_drain_all() used to rely on
> busy waiting to completed throttled I/O requests but this is no longer
> required so we can simplify aio_poll().
> 
> Note that aio_poll() still returns false when aio_notify() was used.  In
> other words, stopping a blocking aio_poll() wait is not considered
> making progress.
> 
> Adjust test-aio /aio/bh/callback-delete/one which assumed aio_poll(ctx,
> true) would immediately return false instead of blocking.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>


Signed-off-by: Alex Bligh <address@hidden>

(if I meant 'Reviewed-By:' please change it!)

> ---
> aio-posix.c      | 5 -----
> aio-win32.c      | 5 -----
> tests/test-aio.c | 1 -
> 3 files changed, 11 deletions(-)
> 
> diff --git a/aio-posix.c b/aio-posix.c
> index bd06f33..f921d4f 100644
> --- a/aio-posix.c
> +++ b/aio-posix.c
> @@ -217,11 +217,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
> 
>     ctx->walking_handlers--;
> 
> -    /* early return if we only have the aio_notify() fd */
> -    if (ctx->pollfds->len == 1) {
> -        return progress;
> -    }
> -
>     /* wait until next event */
>     ret = qemu_poll_ns((GPollFD *)ctx->pollfds->data,
>                          ctx->pollfds->len,
> diff --git a/aio-win32.c b/aio-win32.c
> index f9cfbb7..23f4e5b 100644
> --- a/aio-win32.c
> +++ b/aio-win32.c
> @@ -161,11 +161,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
> 
>     ctx->walking_handlers--;
> 
> -    /* early return if we only have the aio_notify() fd */
> -    if (count == 1) {
> -        return progress;
> -    }
> -
>     /* wait until next event */
>     while (count > 0) {
>         int ret;
> diff --git a/tests/test-aio.c b/tests/test-aio.c
> index c4fe0fc..592721e 100644
> --- a/tests/test-aio.c
> +++ b/tests/test-aio.c
> @@ -195,7 +195,6 @@ static void test_bh_delete_from_cb(void)
>     g_assert(data1.bh == NULL);
> 
>     g_assert(!aio_poll(ctx, false));
> -    g_assert(!aio_poll(ctx, true));
> }
> 
> static void test_bh_delete_from_cb_many(void)
> -- 
> 1.8.3.1
> 
> 
> 

-- 
Alex Bligh