[Qemu-devel] [PATCH v3 3/4] virtio-blk: avoid g_slice_new0() for VirtIOBlockReq and VirtQueueElement

[Stefan Hajnoczi <stefanha@redhat.com>]

In commit de6c8042ec55da18702fa51f09072fcaa315edc3 ("virtio-blk: Avoid
zeroing every request structure") we avoided the 40 KB memset when
allocating VirtIOBlockReq.

The memset was reintroduced in commit
671ec3f056559f22a2531a91dce3a258b9b5eb8a ("virtio-blk: Convert
VirtIOBlockReq.elem to pointer").

It must be fixed again to avoid a performance regression.

Cc: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/block/virtio-blk.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index aec3146..b06a56d 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -31,9 +31,11 @@
 
 static VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s)
 {
-    VirtIOBlockReq *req = g_slice_new0(VirtIOBlockReq);
+    VirtIOBlockReq *req = g_slice_new(VirtIOBlockReq);
     req->dev = s;
-    req->elem = g_slice_new0(VirtQueueElement);
+    req->qiov.size = 0;
+    req->next = NULL;
+    req->elem = g_slice_new(VirtQueueElement);
     return req;
 }
 
-- 
1.9.3