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[Qemu-devel] [PATCH 2/2] virtio-scsi: Optimize virtio_scsi_init_req
From: |
Fam Zheng |
Subject: |
[Qemu-devel] [PATCH 2/2] virtio-scsi: Optimize virtio_scsi_init_req |
Date: |
Thu, 11 Sep 2014 18:16:39 +0800 |
The VirtQueueElement is a very big structure (> 4k), since it will be
initialzed by virtqueue_pop, we can save the expensive zeroing here.
This saves a few nanoseconds 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
virtio-blk read 4k 1 1 217 55673
16
Signed-off-by: Fam Zheng <address@hidden>
---
hw/scsi/virtio-scsi.c | 17 ++++++++++-------
include/hw/virtio/virtio-scsi.h | 1 +
2 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 86aba88..0792529 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -24,12 +24,12 @@
typedef struct VirtIOSCSIReq {
VirtIOSCSI *dev;
VirtQueue *vq;
- VirtQueueElement elem;
QEMUSGList qsgl;
+ QEMUIOVector resp_iov;
+ VirtQueueElement elem;
SCSIRequest *sreq;
size_t resp_size;
enum SCSIXferMode mode;
- QEMUIOVector resp_iov;
union {
VirtIOSCSICmdResp cmd;
VirtIOSCSICtrlTMFResp tmf;
@@ -44,6 +44,7 @@ typedef struct VirtIOSCSIReq {
VirtIOSCSICtrlTMFReq tmf;
VirtIOSCSICtrlANReq an;
} req;
+ uint8_t cdb[VIRTIO_SCSI_CDB_SIZE_MAX];
} VirtIOSCSIReq;
QEMU_BUILD_BUG_ON(offsetof(VirtIOSCSIReq, req.cdb) !=
@@ -68,15 +69,16 @@ 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);
+ const size_t zero_skip = offsetof(VirtIOSCSIReq, elem)
+ + sizeof(VirtQueueElement);
+ req = g_slice_new(VirtIOSCSIReq);
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;
}
@@ -84,7 +86,7 @@ static void virtio_scsi_free_req(VirtIOSCSIReq *req)
{
qemu_iovec_destroy(&req->resp_iov);
qemu_sglist_destroy(&req->qsgl);
- g_free(req);
+ g_slice_free(VirtIOSCSIReq, req);
}
static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
@@ -532,7 +534,8 @@ static void virtio_scsi_set_config(VirtIODevice *vdev,
VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(vdev);
if ((uint32_t) virtio_ldl_p(vdev, &scsiconf->sense_size) >= 65536 ||
- (uint32_t) virtio_ldl_p(vdev, &scsiconf->cdb_size) >= 256) {
+ (uint32_t) virtio_ldl_p(vdev, &scsiconf->cdb_size)
+ >= VIRTIO_SCSI_CDB_SIZE_MAX) {
error_report("bad data written to virtio-scsi configuration space");
exit(1);
}
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index 188a2d9..6e876f4 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -37,6 +37,7 @@
#define VIRTIO_SCSI_VQ_SIZE 128
#define VIRTIO_SCSI_CDB_SIZE 32
+#define VIRTIO_SCSI_CDB_SIZE_MAX 256
#define VIRTIO_SCSI_SENSE_SIZE 96
#define VIRTIO_SCSI_MAX_CHANNEL 0
#define VIRTIO_SCSI_MAX_TARGET 255
--
1.9.3