Commit de6c8042 authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Kevin Wolf
Browse files

virtio-blk: Avoid zeroing every request structure 



The VirtIOBlockRequest structure is about 40 KB in size.  This patch
avoids zeroing every request by only initializing fields that are read.
The other fields are either written to or may not be used at all.

Oprofile shows about 10% of CPU samples in memset called by
virtio_blk_alloc_request().  The workload is
dd if=/dev/vda of=/dev/null iflag=direct bs=8k running concurrently 4
times.  This patch makes memset disappear to the bottom of the profile.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent c53a7285

hw/virtio-blk.c

+3 −1
Original line number Diff line number Diff line
@@ -105,8 +105,10 @@ 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));

    req->dev = s;

    req->qiov.size = 0;

    req->next = NULL;

    return req;

}