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aio: use g_slice_alloc() for AIOCB pooling 

AIO control blocks are frequently acquired and released because each aio
request involves at least one AIOCB.  Therefore, we pool them to avoid
heap allocation overhead.

The problem with the freelist approach in AIOPool is thread-safety.  If
we want BlockDriverStates to associate with AioContexts that execute in
multiple threads, then a global freelist becomes a problem.

This patch drops the freelist and instead uses g_slice_alloc() which is
tuned for per-thread fixed-size object pools.  qemu_aio_get() and
qemu_aio_release() are now thread-safe.

Note that the change from g_malloc0() to g_slice_alloc() should be safe
since the freelist reuse case doesn't zero the AIOCB either.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2012-10-31 16:34:36 +01:00 committed by Kevin Wolf
parent 8c82e9a433
commit d37c975fb1
2 changed files with 4 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
block.c
View File

@ -3909,13 +3909,8 @@ void *qemu_aio_get(AIOPool *pool, BlockDriverState *bs,
{
BlockDriverAIOCB *acb;
if (pool->free_aiocb) {
acb = pool->free_aiocb;
pool->free_aiocb = acb->next;
} else {
acb = g_malloc0(pool->aiocb_size);
acb->pool = pool;
}
acb = g_slice_alloc(pool->aiocb_size);
acb->pool = pool;
acb->bs = bs;
acb->cb = cb;
acb->opaque = opaque;
@ -3924,10 +3919,8 @@ void *qemu_aio_get(AIOPool *pool, BlockDriverState *bs,
void qemu_aio_release(void *p)
{
BlockDriverAIOCB *acb = (BlockDriverAIOCB *)p;
AIOPool *pool = acb->pool;
acb->next = pool->free_aiocb;
pool->free_aiocb = acb;
BlockDriverAIOCB *acb = p;
g_slice_free1(acb->pool->aiocb_size, acb);
}
/**************************************************************/

2
qemu-aio.h
View File

@ -24,7 +24,6 @@ typedef void BlockDriverCompletionFunc(void *opaque, int ret);
typedef struct AIOPool {
void (*cancel)(BlockDriverAIOCB *acb);
size_t aiocb_size;
BlockDriverAIOCB *free_aiocb;
} AIOPool;
struct BlockDriverAIOCB {
@ -32,7 +31,6 @@ struct BlockDriverAIOCB {
BlockDriverState *bs;
BlockDriverCompletionFunc *cb;
void *opaque;
BlockDriverAIOCB *next;
};
void *qemu_aio_get(AIOPool *pool, BlockDriverState *bs,