On 3/2/23 1:58 AM, Christophe JAILLET wrote:
> 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>
Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
> ---
> 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)
--
BR,
Muhammad Usama Anjum
