From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34610) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XYwUy-0006sk-3R for qemu-devel@nongnu.org; Tue, 30 Sep 2014 08:25:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XYwUp-0002yQ-0N for qemu-devel@nongnu.org; Tue, 30 Sep 2014 08:25:44 -0400 Received: from mail-wg0-x22b.google.com ([2a00:1450:400c:c00::22b]:37147) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XYwUo-0002xy-L0 for qemu-devel@nongnu.org; Tue, 30 Sep 2014 08:25:34 -0400 Received: by mail-wg0-f43.google.com with SMTP id a1so3551314wgh.26 for ; Tue, 30 Sep 2014 05:25:28 -0700 (PDT) Sender: Paolo Bonzini From: Paolo Bonzini Date: Tue, 30 Sep 2014 14:24:42 +0200 Message-Id: <1412079919-18857-3-git-send-email-pbonzini@redhat.com> In-Reply-To: <1412079919-18857-1-git-send-email-pbonzini@redhat.com> References: <1412079919-18857-1-git-send-email-pbonzini@redhat.com> Subject: [Qemu-devel] [PULL 02/39] virtio-scsi: Optimize virtio_scsi_init_req List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Fam Zheng From: Fam Zheng The VirtQueueElement is a very big structure (>48k!), since it will be initialzed by virtqueue_pop, we can save the expensive zeroing here. This saves a few microseconds per request in my test: [fio-test] rw bs iodepth jobs bw iops latency -------------------------------------------------------------------------------------------- Before read 4k 1 1 110 28269 34 After read 4k 1 1 131 33745 28 Whereas, virtio-blk read 4k 1 1 217 55673 16 Signed-off-by: Fam Zheng Signed-off-by: Paolo Bonzini --- hw/scsi/virtio-scsi.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c index 86aba88..f0d21a3 100644 --- a/hw/scsi/virtio-scsi.c +++ b/hw/scsi/virtio-scsi.c @@ -24,12 +24,19 @@ typedef struct VirtIOSCSIReq { VirtIOSCSI *dev; VirtQueue *vq; - VirtQueueElement elem; QEMUSGList qsgl; + QEMUIOVector resp_iov; + + /* Note: + * - fields before elem are initialized by virtio_scsi_init_req; + * - elem is uninitialized at the time of allocation. + * - fields after elem are zeroed by virtio_scsi_init_req. + * */ + + VirtQueueElement elem; SCSIRequest *sreq; size_t resp_size; enum SCSIXferMode mode; - QEMUIOVector resp_iov; union { VirtIOSCSICmdResp cmd; VirtIOSCSICtrlTMFResp tmf; @@ -68,23 +75,26 @@ static inline SCSIDevice *virtio_scsi_device_find(VirtIOSCSI *s, uint8_t *lun) static VirtIOSCSIReq *virtio_scsi_init_req(VirtIOSCSI *s, VirtQueue *vq) { VirtIOSCSIReq *req; - VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(s); - - req = g_malloc0(sizeof(*req) + vs->cdb_size); + VirtIOSCSICommon *vs = (VirtIOSCSICommon *)s; + const size_t zero_skip = offsetof(VirtIOSCSIReq, elem) + + sizeof(VirtQueueElement); + req = g_slice_alloc(sizeof(*req) + vs->cdb_size); req->vq = vq; req->dev = s; - req->sreq = NULL; qemu_sglist_init(&req->qsgl, DEVICE(s), 8, &address_space_memory); qemu_iovec_init(&req->resp_iov, 1); + memset((uint8_t *)req + zero_skip, 0, sizeof(*req) - zero_skip); return req; } static void virtio_scsi_free_req(VirtIOSCSIReq *req) { + VirtIOSCSICommon *vs = (VirtIOSCSICommon *)req->dev; + qemu_iovec_destroy(&req->resp_iov); qemu_sglist_destroy(&req->qsgl); - g_free(req); + g_slice_free1(sizeof(*req) + vs->cdb_size, req); } static void virtio_scsi_complete_req(VirtIOSCSIReq *req) -- 1.8.3.1