From patchwork Wed Nov 18 14:41:22 2009 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [PATCH] qemu-kvm: clear only essential parts of VirtIOBlockReq on object allocation - RESUBMIT From: Saul Tamari X-Patchwork-Id: 38748 Message-Id: <20091118144122.GC19099@localhost.localdomain> To: Anthony Liguori Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org Date: Wed, 18 Nov 2009 16:41:22 +0200 ok, Below is the patch. This time resent with mutt and hopefully without whitespace changes. -------------------------------------------------------------------- This patch reduces the amount of memory being cleared on every virtio-blk IO operation. Improve number of IOPS when using avirtio-blk device. On every virtio-blk IO command passed to QEMU, virtio_blk_alloc_request() allocates and clears (with qemu_mallocz()) a VirtIOBlockReq object. The sizeof(VirtIOBlockReq) equals 41040 bytes on my x86-64 machine. By moving the 'elem' variable to the end of VirtIOBlockReq and clearing only upto the address of the 'elem.in_addr' field, the memset() call now clears only 80 bytes. Signed-off-by: Saul Tamari ------------------------------------------------- diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c index 2630b99..de74b00 100644 --- a/hw/virtio-blk.c +++ b/hw/virtio-blk.c @@ -79,12 +79,13 @@ static inline void virtio_identify_template(struct virtio_blk_config *bc) typedef struct VirtIOBlockReq { VirtIOBlock *dev; - VirtQueueElement elem; struct virtio_blk_inhdr *in; struct virtio_blk_outhdr *out; struct virtio_scsi_inhdr *scsi; QEMUIOVector qiov; struct VirtIOBlockReq *next; + /* Members that need clearing, must be added prior to elem */ + VirtQueueElement elem; } VirtIOBlockReq; static void virtio_blk_req_complete(VirtIOBlockReq *req, int status) @@ -139,7 +140,8 @@ static void virtio_blk_flush_complete(void *opaque, int ret) static VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s) { - VirtIOBlockReq *req = qemu_mallocz(sizeof(*req)); + VirtIOBlockReq *req = qemu_malloc(sizeof(*req)); + memset(req, 0, offsetof(VirtIOBlockReq, elem.in_addr[0])); req->dev = s; return req; }