Il 31/10/2012 16:34, Stefan Hajnoczi ha scritto:
> 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 <stefa...@redhat.com>
> ---
> block.c | 15 ++++-----------
> qemu-aio.h | 2 --
> 2 files changed, 4 insertions(+), 13 deletions(-)
>
> diff --git a/block.c b/block.c
> index da1fdca..ea0f7d8 100644
> --- a/block.c
> +++ b/block.c
> @@ -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);
> }
>
> /**************************************************************/
> diff --git a/qemu-aio.h b/qemu-aio.h
> index 111b0b3..b29c509 100644
> --- a/qemu-aio.h
> +++ b/qemu-aio.h
> @@ -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,
>
Reviewed-by: Paolo Bonzini <pbonz...@redhat.com>
