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[Qemu-devel] Re: [PATCH] qemu-kvm: clear only essential parts of VirtIOB
From: |
Saul Tamari |
Subject: |
[Qemu-devel] Re: [PATCH] qemu-kvm: clear only essential parts of VirtIOBlockReq on object allocation - RESUBMIT |
Date: |
Wed, 18 Nov 2009 16:41:22 +0200 |
User-agent: |
Mutt/1.5.19 (2009-01-05) |
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 <address@hidden>
-------------------------------------------------
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;
}