On Sat, Feb 18, 2023 at 09:10:31AM +0100, Christophe JAILLET wrote:
Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size of 'struct virtqueue'
from 72 to 68 bytes.
It saves a few bytes of memory.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
LGTM!
Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Using pahole
Before:
======
struct virtqueue {
struct list_head list; /* 0 16 */
void (*callback)(struct virtqueue *); /* 16 8 */
const char * name; /* 24 8 */
struct virtio_device * vdev; /* 32 8 */
unsigned int index; /* 40 4 */
unsigned int num_free; /* 44 4 */
unsigned int num_max; /* 48 4 */
/* XXX 4 bytes hole, try to pack */
void * priv; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
bool reset; /* 64 1 */
/* size: 72, cachelines: 2, members: 9 */
/* sum members: 61, holes: 1, sum holes: 4 */
/* padding: 7 */
/* last cacheline: 8 bytes */
};
After:
=====
struct virtqueue {
struct list_head list; /* 0 16 */
void (*callback)(struct virtqueue *); /* 16 8 */
const char * name; /* 24 8 */
struct virtio_device * vdev; /* 32 8 */
unsigned int index; /* 40 4 */
unsigned int num_free; /* 44 4 */
unsigned int num_max; /* 48 4 */
bool reset; /* 52 1 */
/* XXX 3 bytes hole, try to pack */
void * priv; /* 56 8 */
/* size: 64, cachelines: 1, members: 9 */
/* sum members: 61, holes: 1, sum holes: 3 */
};
---
include/linux/virtio.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 6ac2655500dc..9439ae898310 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -35,8 +35,8 @@ struct virtqueue {
unsigned int index;
unsigned int num_free;
unsigned int num_max;
- void *priv;
bool reset;
+ void *priv;
};
int virtqueue_add_outbuf(struct virtqueue *vq,
--
2.34.1
