From 0a9052726f50932d311edf0e19c0d195d02e20b9 Mon Sep 17 00:00:00 2001 From: Fam Zheng Date: Wed, 26 Nov 2014 08:07:57 +0100 Subject: [PATCH 2/4] virtio-scsi: Optimize virtio_scsi_init_req Message-id: <1416989278-17785-3-git-send-email-famz@redhat.com> Patchwork-id: 62593 O-Subject: [RHEL-7.1 qemu-kvm-rhev PATCH v2 2/3] virtio-scsi: Optimize virtio_scsi_init_req Bugzilla: 1141656 RH-Acked-by: Stefan Hajnoczi RH-Acked-by: Laszlo Ersek RH-Acked-by: Paolo Bonzini 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 (cherry picked from commit faf1e1fb4cdd3f1f71c948cb53e7d50f0798a202) Signed-off-by: Fam Zheng Signed-off-by: Miroslav Rezanina --- 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 9e6592f..9ab956e 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