From d37c975fb134e1b16f09b4e6545e2c0591fb6455 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 31 Oct 2012 16:34:36 +0100 Subject: [PATCH] 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 Reviewed-by: Paolo Bonzini Signed-off-by: Kevin Wolf --- block.c | 15 ++++----------- qemu-aio.h | 2 -- 2 files changed, 4 insertions(+), 13 deletions(-) diff --git a/block.c b/block.c index da1fdca0e0..ea0f7d8367 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 111b0b3f0a..b29c509f27 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, -- 2.11.0