* [Qemu-devel] [PATCH v3 1/2] scsi: Optimize scsi_req_alloc
2014-09-16 7:20 [Qemu-devel] [PATCH v3 0/2] virtio-scsi: Optimizing request allocation Fam Zheng
@ 2014-09-16 7:20 ` Fam Zheng
2014-09-16 7:20 ` [Qemu-devel] [PATCH v3 2/2] virtio-scsi: Optimize virtio_scsi_init_req Fam Zheng
2014-09-16 8:19 ` [Qemu-devel] [PATCH v3 0/2] virtio-scsi: Optimizing request allocation Paolo Bonzini
2 siblings, 0 replies; 4+ messages in thread
From: Fam Zheng @ 2014-09-16 7:20 UTC (permalink / raw)
To: qemu-devel; +Cc: Paolo Bonzini
Zeroing sense buffer for each scsi request is not efficient, we can just
leave it uninitialized because sense_len is set to 0.
Move the implicitly zeroed fields to the end of the structure and use a
partial memset.
The explicitly initialized fields (by scsi_req_alloc or scsi_req_new)
are moved to the beginning of the structure, before sense buffer, to
skip the memset.
Also change g_malloc0 to g_slice_alloc.
Signed-off-by: Fam Zheng <famz@redhat.com>
---
hw/scsi/scsi-bus.c | 8 +++++---
include/hw/scsi/scsi.h | 21 ++++++++++++++-------
2 files changed, 19 insertions(+), 10 deletions(-)
diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
index 954c607..af293b5 100644
--- a/hw/scsi/scsi-bus.c
+++ b/hw/scsi/scsi-bus.c
@@ -551,8 +551,11 @@ SCSIRequest *scsi_req_alloc(const SCSIReqOps *reqops, SCSIDevice *d,
SCSIRequest *req;
SCSIBus *bus = scsi_bus_from_device(d);
BusState *qbus = BUS(bus);
+ const int memset_off = offsetof(SCSIRequest, sense)
+ + sizeof(req->sense);
- req = g_malloc0(reqops->size);
+ req = g_slice_alloc(reqops->size);
+ memset((uint8_t *)req + memset_off, 0, reqops->size - memset_off);
req->refcount = 1;
req->bus = bus;
req->dev = d;
@@ -560,7 +563,6 @@ SCSIRequest *scsi_req_alloc(const SCSIReqOps *reqops, SCSIDevice *d,
req->lun = lun;
req->hba_private = hba_private;
req->status = -1;
- req->sense_len = 0;
req->ops = reqops;
object_ref(OBJECT(d));
object_ref(OBJECT(qbus->parent));
@@ -1603,7 +1605,7 @@ void scsi_req_unref(SCSIRequest *req)
}
object_unref(OBJECT(req->dev));
object_unref(OBJECT(qbus->parent));
- g_free(req);
+ g_slice_free1(req->ops->size, req);
}
}
diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
index 2e3a8f9..6271ad3 100644
--- a/include/hw/scsi/scsi.h
+++ b/include/hw/scsi/scsi.h
@@ -50,17 +50,24 @@ struct SCSIRequest {
uint32_t tag;
uint32_t lun;
uint32_t status;
+ void *hba_private;
size_t resid;
SCSICommand cmd;
+
+ /* Note:
+ * - fields before sense are initialized by scsi_req_alloc;
+ * - sense[] is uninitialized;
+ * - fields after sense are memset to 0 by scsi_req_alloc.
+ * */
+
+ uint8_t sense[SCSI_SENSE_BUF_SIZE];
+ uint32_t sense_len;
+ bool enqueued;
+ bool io_canceled;
+ bool retry;
+ bool dma_started;
BlockDriverAIOCB *aiocb;
QEMUSGList *sg;
- bool dma_started;
- uint8_t sense[SCSI_SENSE_BUF_SIZE];
- uint32_t sense_len;
- bool enqueued;
- bool io_canceled;
- bool retry;
- void *hba_private;
QTAILQ_ENTRY(SCSIRequest) next;
};
--
1.9.3
^ permalink raw reply related [flat|nested] 4+ messages in thread* [Qemu-devel] [PATCH v3 2/2] virtio-scsi: Optimize virtio_scsi_init_req
2014-09-16 7:20 [Qemu-devel] [PATCH v3 0/2] virtio-scsi: Optimizing request allocation Fam Zheng
2014-09-16 7:20 ` [Qemu-devel] [PATCH v3 1/2] scsi: Optimize scsi_req_alloc Fam Zheng
@ 2014-09-16 7:20 ` Fam Zheng
2014-09-16 8:19 ` [Qemu-devel] [PATCH v3 0/2] virtio-scsi: Optimizing request allocation Paolo Bonzini
2 siblings, 0 replies; 4+ messages in thread
From: Fam Zheng @ 2014-09-16 7:20 UTC (permalink / raw)
To: qemu-devel; +Cc: 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 <famz@redhat.com>
---
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)
--
1.9.3
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [Qemu-devel] [PATCH v3 0/2] virtio-scsi: Optimizing request allocation
2014-09-16 7:20 [Qemu-devel] [PATCH v3 0/2] virtio-scsi: Optimizing request allocation Fam Zheng
2014-09-16 7:20 ` [Qemu-devel] [PATCH v3 1/2] scsi: Optimize scsi_req_alloc Fam Zheng
2014-09-16 7:20 ` [Qemu-devel] [PATCH v3 2/2] virtio-scsi: Optimize virtio_scsi_init_req Fam Zheng
@ 2014-09-16 8:19 ` Paolo Bonzini
2 siblings, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2014-09-16 8:19 UTC (permalink / raw)
To: Fam Zheng, qemu-devel
Il 16/09/2014 09:20, Fam Zheng ha scritto:
> v3: Small tweak on "cmd" in 1/2 and "sreq" in 2/2.
>
> Zeroing is relatively expensive since we have big request structures.
> VirtQueueElement (>48k!) and sense_buf (256 bytes) are two points to look at.
>
> This visibly reduces overhead of request handling when testing with the
> unmerged "null" driver and virtio-scsi dataplane. Before, the issue is very
> obvious with perf top:
>
> perf top -G -p `pidof qemu-system-x86_64`
> -----------------------------------------
> + 16.50% libc-2.17.so [.] __memset_sse2
> + 2.28% libc-2.17.so [.] _int_malloc
> + 2.25% [vdso] [.] 0x0000000000000cd1
> + 2.02% [kernel] [k] _raw_spin_lock_irqsave
> + 1.97% libpthread-2.17.so [.] pthread_mutex_lock
> + 1.87% libpthread-2.17.so [.] pthread_mutex_unlock
> + 1.81% [kernel] [k] fget_light
> + 1.70% libc-2.17.so [.] malloc
>
> After, the high __memset_sse2 and _int_malloc is gone:
>
> perf top -G -p `pidof qemu-system-x86_64`
> -----------------------------------------
> + 4.20% [kernel] [k] vcpu_enter_guest
> + 3.97% [kernel] [k] vmx_vcpu_run
> + 2.63% [kernel] [k] _raw_spin_lock_irqsave
> + 1.72% [kernel] [k] native_read_msr_safe
> + 1.65% [kernel] [k] __srcu_read_lock
> + 1.64% [kernel] [k] _raw_spin_unlock_irqrestore
> + 1.57% [vdso] [.] 0x00000000000008d8
> + 1.49% libc-2.17.so [.] _int_malloc
> + 1.29% libpthread-2.17.so [.] pthread_mutex_unlock
> + 1.26% [kernel] [k] native_write_msr_safe
>
> See the commit message of patch 2 for some fio test data.
Thanks, applied to scsi-next.
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread