Re: [PATCH v5 05/20] aio-wait.h: introduce AIO_WAIT_WHILE_UNLOCKED

[Stefan Hajnoczi]

On Tue, Feb 08, 2022 at 09:34:58AM -0500, Emanuele Giuseppe Esposito wrote:
> Same as AIO_WAIT_WHILE macro, but if we are in the Main loop
> do not release and then acquire ctx_ 's aiocontext.
> 
> Once all Aiocontext locks go away, this macro will replace
> AIO_WAIT_WHILE.
> 
> Signed-off-by: Emanuele Giuseppe Esposito 
> ---
>  include/block/aio-wait.h | 15 +++
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
> index b39eefb38d..ff27fe4eab 100644
> --- a/include/block/aio-wait.h
> +++ b/include/block/aio-wait.h
> @@ -59,10 +59,11 @@ typedef struct {
>  extern AioWait global_aio_wait;
>  
>  /**
> - * AIO_WAIT_WHILE:
> + * _AIO_WAIT_WHILE:
>   * @ctx: the aio context, or NULL if multiple aio contexts (for which the
>   *   caller does not hold a lock) are involved in the polling condition.
>   * @cond: wait while this conditional expression is true
> + * @unlock: whether to unlock and then lock again @ctx

Please document that this only applies when waiting for another
AioContext from the main loop thread. It's ignored otherwise.


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[PATCH v5 05/20] aio-wait.h: introduce AIO_WAIT_WHILE_UNLOCKED

[Emanuele Giuseppe Esposito]

Same as AIO_WAIT_WHILE macro, but if we are in the Main loop
do not release and then acquire ctx_ 's aiocontext.

Once all Aiocontext locks go away, this macro will replace
AIO_WAIT_WHILE.

Signed-off-by: Emanuele Giuseppe Esposito 
---
 include/block/aio-wait.h | 15 +++
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
index b39eefb38d..ff27fe4eab 100644
--- a/include/block/aio-wait.h
+++ b/include/block/aio-wait.h
@@ -59,10 +59,11 @@ typedef struct {
 extern AioWait global_aio_wait;
 
 /**
- * AIO_WAIT_WHILE:
+ * _AIO_WAIT_WHILE:
  * @ctx: the aio context, or NULL if multiple aio contexts (for which the
  *   caller does not hold a lock) are involved in the polling condition.
  * @cond: wait while this conditional expression is true
+ * @unlock: whether to unlock and then lock again @ctx
  *
  * Wait while a condition is true.  Use this to implement synchronous
  * operations that require event loop activity.
@@ -75,7 +76,7 @@ extern AioWait global_aio_wait;
  * wait on conditions between two IOThreads since that could lead to deadlock,
  * go via the main loop instead.
  */
-#define AIO_WAIT_WHILE(ctx, cond) ({   \
+#define _AIO_WAIT_WHILE(ctx, cond, unlock) ({  \
 bool waited_ = false;  \
 AioWait *wait_ = _aio_wait; \
 AioContext *ctx_ = (ctx);  \
@@ -90,11 +91,11 @@ extern AioWait global_aio_wait;
 assert(qemu_get_current_aio_context() ==   \
qemu_get_aio_context());\
 while ((cond)) {   \
-if (ctx_) {\
+if (unlock && ctx_) {  \
 aio_context_release(ctx_); \
 }  \
 aio_poll(qemu_get_aio_context(), true);\
-if (ctx_) {\
+if (unlock && ctx_) {  \
 aio_context_acquire(ctx_); \
 }  \
 waited_ = true;\
@@ -103,6 +104,12 @@ extern AioWait global_aio_wait;
 qatomic_dec(_->num_waiters);  \
 waited_; })
 
+#define AIO_WAIT_WHILE(ctx, cond)  \
+_AIO_WAIT_WHILE(ctx, cond, true)
+
+#define AIO_WAIT_WHILE_UNLOCKED(ctx, cond) \
+_AIO_WAIT_WHILE(ctx, cond, false)
+
 /**
  * aio_wait_kick:
  * Wake up the main thread if it is waiting on AIO_WAIT_WHILE().  During
-- 
2.31.1