Re: [Qemu-devel] [PATCH 7/7] curl: do not do aio_poll when waiting for a free CURLState

[Jeff Cody <jcody@redhat.com>]

On Wed, May 10, 2017 at 04:32:05PM +0200, Paolo Bonzini wrote:
> Instead, put the CURLAIOCB on a wait list; curl_clean_state will
> wake the corresponding coroutine.
> 
> Because of CURL's callback-based structure, we cannot easily convert
> everything to CoMutex/CoQueue; keeping the QemuMutex is simpler.
> However, CoQueue is a simple wrapper around a linked list, so we can
> use QSIMPLEQ easily to open-code a CoQueue that has a QemuMutex's
> protection instead of a CoMutex's.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/curl.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/block/curl.c b/block/curl.c
> index 80870bd60c..4ccdf63510 100644
> --- a/block/curl.c
> +++ b/block/curl.c
> @@ -98,6 +98,8 @@ typedef struct CURLAIOCB {
>  
>      size_t start;
>      size_t end;
> +
> +    QSIMPLEQ_ENTRY(CURLAIOCB) next;
>  } CURLAIOCB;
>  
>  typedef struct CURLSocket {
> @@ -133,6 +135,7 @@ typedef struct BDRVCURLState {
>      bool accept_range;
>      AioContext *aio_context;
>      QemuMutex mutex;
> +    QSIMPLEQ_HEAD(, CURLAIOCB) free_state_waitq;
>      char *username;
>      char *password;
>      char *proxyusername;
> @@ -532,6 +535,7 @@ static int curl_init_state(BDRVCURLState *s, CURLState *state)
>  /* Called with s->mutex held.  */
>  static void curl_clean_state(CURLState *s)
>  {
> +    CURLAIOCB *next;
>      int j;
>      for (j=0; j<CURL_NUM_ACB; j++) {
>          assert(!s->acb[j]);
> @@ -548,6 +552,14 @@ static void curl_clean_state(CURLState *s)
>      }
>  
>      s->in_use = 0;
> +
> +    next = QSIMPLEQ_FIRST(&s->s->free_state_waitq);
> +    if (next) {
> +        QSIMPLEQ_REMOVE_HEAD(&s->s->free_state_waitq, next);
> +        qemu_mutex_unlock(&s->s->mutex);
> +        aio_co_wake(next->co);
> +        qemu_mutex_lock(&s->s->mutex);
> +    }
>  }
>  
>  static void curl_parse_filename(const char *filename, QDict *options,
> @@ -744,6 +756,7 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
>  
>      DPRINTF("CURL: Opening %s\n", file);
>      qemu_mutex_init(&s->mutex);
> +    QSIMPLEQ_INIT(&s->free_state_waitq);
>      s->aio_context = bdrv_get_aio_context(bs);
>      s->url = g_strdup(file);
>      qemu_mutex_lock(&s->mutex);
> @@ -843,8 +856,9 @@ static void curl_setup_preadv(BlockDriverState *bs, CURLAIOCB *acb)
>          if (state) {
>              break;
>          }
> +        QSIMPLEQ_INSERT_TAIL(&s->free_state_waitq, acb, next);
>          qemu_mutex_unlock(&s->mutex);
> -        aio_poll(bdrv_get_aio_context(bs), true);
> +        qemu_coroutine_yield();
>          qemu_mutex_lock(&s->mutex);
>      }
>  
> -- 
> 2.12.2
>

Reviewed-by: Jeff Cody <jcody@redhat.com>