[1/2] aio: allow to wait for coroutine pool from different coroutine
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Message ID 20200610144129.27659-2-den@openvz.org
State New
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Series
  • qcow2: seriously improve savevm performance
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Commit Message

Denis V. Lunev June 10, 2020, 2:41 p.m. UTC
The patch preserves the constraint that the only waiter is allowed.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
CC: Denis Plotnikov <dplotnikov@virtuozzo.com>
---
 block/aio_task.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Vladimir Sementsov-Ogievskiy June 10, 2020, 3:10 p.m. UTC | #1
10.06.2020 17:41, Denis V. Lunev wrote:
> The patch preserves the constraint that the only waiter is allowed.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Max Reitz <mreitz@redhat.com>
> CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> CC: Denis Plotnikov <dplotnikov@virtuozzo.com>
> ---
>   block/aio_task.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/block/aio_task.c b/block/aio_task.c
> index 88989fa248..f338049147 100644
> --- a/block/aio_task.c
> +++ b/block/aio_task.c
> @@ -27,7 +27,7 @@
>   #include "block/aio_task.h"
>   
>   struct AioTaskPool {
> -    Coroutine *main_co;
> +    Coroutine *wake_co;
>       int status;
>       int max_busy_tasks;
>       int busy_tasks;
> @@ -54,15 +54,15 @@ static void coroutine_fn aio_task_co(void *opaque)
>   
>       if (pool->waiting) {
>           pool->waiting = false;
> -        aio_co_wake(pool->main_co);
> +        aio_co_wake(pool->wake_co);
>       }
>   }
>   
>   void coroutine_fn aio_task_pool_wait_one(AioTaskPool *pool)
>   {
>       assert(pool->busy_tasks > 0);
> -    assert(qemu_coroutine_self() == pool->main_co);
>   
> +    pool->wake_co = qemu_coroutine_self();
>       pool->waiting = true;
>       qemu_coroutine_yield();
>   
> @@ -98,7 +98,7 @@ AioTaskPool *coroutine_fn aio_task_pool_new(int max_busy_tasks)
>   {
>       AioTaskPool *pool = g_new0(AioTaskPool, 1);
>   
> -    pool->main_co = qemu_coroutine_self();
> +    pool->wake_co = NULL;
>       pool->max_busy_tasks = max_busy_tasks;
>   
>       return pool;
> 

With such approach, if several coroutines will wait simultaneously, the only one will be finally woken and other will hang.

I think, we should use CoQueue here: CoQueue instead of wake_co, qemu_co_queue_wait in wait_one, and qemu_co_queue_next instead of aio_co_wake.
Denis V. Lunev June 10, 2020, 4:52 p.m. UTC | #2
On 6/10/20 6:10 PM, Vladimir Sementsov-Ogievskiy wrote:
> 10.06.2020 17:41, Denis V. Lunev wrote:
>> The patch preserves the constraint that the only waiter is allowed.
>>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Kevin Wolf <kwolf@redhat.com>
>> CC: Max Reitz <mreitz@redhat.com>
>> CC: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> CC: Denis Plotnikov <dplotnikov@virtuozzo.com>
>> ---
>>   block/aio_task.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/block/aio_task.c b/block/aio_task.c
>> index 88989fa248..f338049147 100644
>> --- a/block/aio_task.c
>> +++ b/block/aio_task.c
>> @@ -27,7 +27,7 @@
>>   #include "block/aio_task.h"
>>     struct AioTaskPool {
>> -    Coroutine *main_co;
>> +    Coroutine *wake_co;
>>       int status;
>>       int max_busy_tasks;
>>       int busy_tasks;
>> @@ -54,15 +54,15 @@ static void coroutine_fn aio_task_co(void *opaque)
>>         if (pool->waiting) {
>>           pool->waiting = false;
>> -        aio_co_wake(pool->main_co);
>> +        aio_co_wake(pool->wake_co);
>>       }
>>   }
>>     void coroutine_fn aio_task_pool_wait_one(AioTaskPool *pool)
>>   {
>>       assert(pool->busy_tasks > 0);
>> -    assert(qemu_coroutine_self() == pool->main_co);
>>   +    pool->wake_co = qemu_coroutine_self();
>>       pool->waiting = true;
>>       qemu_coroutine_yield();
>>   @@ -98,7 +98,7 @@ AioTaskPool *coroutine_fn aio_task_pool_new(int
>> max_busy_tasks)
>>   {
>>       AioTaskPool *pool = g_new0(AioTaskPool, 1);
>>   -    pool->main_co = qemu_coroutine_self();
>> +    pool->wake_co = NULL;
>>       pool->max_busy_tasks = max_busy_tasks;
>>         return pool;
>>
>
> With such approach, if several coroutines will wait simultaneously,
> the only one will be finally woken and other will hang.
>
> I think, we should use CoQueue here: CoQueue instead of wake_co,
> qemu_co_queue_wait in wait_one, and qemu_co_queue_next instead of
> aio_co_wake.
>
>
I will make a check, but for now it would be enough to
add
  assert(!pool->waiting);
at the beginning of aio_task_pool_wait_one

Den

Patch
diff mbox series

diff --git a/block/aio_task.c b/block/aio_task.c
index 88989fa248..f338049147 100644
--- a/block/aio_task.c
+++ b/block/aio_task.c
@@ -27,7 +27,7 @@ 
 #include "block/aio_task.h"
 
 struct AioTaskPool {
-    Coroutine *main_co;
+    Coroutine *wake_co;
     int status;
     int max_busy_tasks;
     int busy_tasks;
@@ -54,15 +54,15 @@  static void coroutine_fn aio_task_co(void *opaque)
 
     if (pool->waiting) {
         pool->waiting = false;
-        aio_co_wake(pool->main_co);
+        aio_co_wake(pool->wake_co);
     }
 }
 
 void coroutine_fn aio_task_pool_wait_one(AioTaskPool *pool)
 {
     assert(pool->busy_tasks > 0);
-    assert(qemu_coroutine_self() == pool->main_co);
 
+    pool->wake_co = qemu_coroutine_self();
     pool->waiting = true;
     qemu_coroutine_yield();
 
@@ -98,7 +98,7 @@  AioTaskPool *coroutine_fn aio_task_pool_new(int max_busy_tasks)
 {
     AioTaskPool *pool = g_new0(AioTaskPool, 1);
 
-    pool->main_co = qemu_coroutine_self();
+    pool->wake_co = NULL;
     pool->max_busy_tasks = max_busy_tasks;
 
     return pool;