Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size from 112 to 96 bytes.
This should have no real impact on memory allocation because 'struct
spi_message' is mostly used on stack, but it can save a few cycles
when the structure is initialized with spi_message_init() and co.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
Using pahole
Before:
======
struct spi_message {
struct list_head transfers; /* 0 16 */
struct spi_device * spi; /* 16 8 */
unsigned int is_dma_mapped:1; /* 24: 0 4 */
/* XXX 31 bits hole, try to pack */
/* XXX 4 bytes hole, try to pack */
void (*complete)(void *); /* 32 8 */
void * context; /* 40 8 */
unsigned int frame_length; /* 48 4 */
unsigned int actual_length; /* 52 4 */
int status; /* 56 4 */
/* XXX 4 bytes hole, try to pack */
/* --- cacheline 1 boundary (64 bytes) --- */
struct list_head queue; /* 64 16 */
void * state; /* 80 8 */
struct list_head resources; /* 88 16 */
bool prepared; /* 104 1 */
/* size: 112, cachelines: 2, members: 12 */
/* sum members: 93, holes: 2, sum holes: 8 */
/* sum bitfield members: 1 bits, bit holes: 1, sum bit holes: 31 bits */
/* padding: 7 */
/* last cacheline: 48 bytes */
};
After:
=====
struct spi_message {
struct list_head transfers; /* 0 16 */
struct spi_device * spi; /* 16 8 */
unsigned int is_dma_mapped:1; /* 24: 0 4 */
/* XXX 7 bits hole, try to pack */
/* Bitfield combined with next fields */
bool prepared; /* 25 1 */
/* XXX 2 bytes hole, try to pack */
int status; /* 28 4 */
void (*complete)(void *); /* 32 8 */
void * context; /* 40 8 */
unsigned int frame_length; /* 48 4 */
unsigned int actual_length; /* 52 4 */
struct list_head queue; /* 56 16 */
/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
void * state; /* 72 8 */
struct list_head resources; /* 80 16 */
/* size: 96, cachelines: 2, members: 12 */
/* sum members: 93, holes: 1, sum holes: 2 */
/* sum bitfield members: 1 bits, bit holes: 1, sum bit holes: 7 bits */
/* last cacheline: 32 bytes */
};
---
include/linux/spi/spi.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 4fa26b9a3572..bdb35a91b4bf 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -1093,6 +1093,9 @@ struct spi_message {
unsigned is_dma_mapped:1;
+ /* spi_prepare_message() was called for this message */
+ bool prepared;
+
/* REVISIT: we might want a flag affecting the behavior of the
* last transfer ... allowing things like "read 16 bit length L"
* immediately followed by "read L bytes". Basically imposing
@@ -1105,11 +1108,11 @@ struct spi_message {
*/
/* Completion is reported through a callback */
+ int status;
void (*complete)(void *context);
void *context;
unsigned frame_length;
unsigned actual_length;
- int status;
/* For optional use by whatever driver currently owns the
* spi_message ... between calls to spi_async and then later
@@ -1120,9 +1123,6 @@ struct spi_message {
/* List of spi_res reources when the spi message is processed */
struct list_head resources;
-
- /* spi_prepare_message() was called for this message */
- bool prepared;
};
static inline void spi_message_init_no_memset(struct spi_message *m)
--
2.34.1
