* [PATCH] spi: Reorder fields in 'struct spi_transfer'
@ 2023-02-14 10:34 Christophe JAILLET
2023-02-14 21:10 ` Mark Brown
0 siblings, 1 reply; 2+ messages in thread
From: Christophe JAILLET @ 2023-02-14 10:34 UTC (permalink / raw)
To: Mark Brown, Richard Cochran
Cc: linux-kernel, kernel-janitors, Christophe JAILLET, linux-spi, netdev
Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size from 144 to 128 bytes.
Turn 'timestamped' into a bitfield so that it can be easily merged with
some other bifields and move 'error'.
This should have no real impact on memory allocation because 'struct
spi_transfer' is mostly used on stack, but it can save a few cycles
when the structure is initialized or copied.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
Using pahole
Before:
======
struct spi_transfer {
const void * tx_buf; /* 0 8 */
void * rx_buf; /* 8 8 */
unsigned int len; /* 16 4 */
/* XXX 4 bytes hole, try to pack */
dma_addr_t tx_dma; /* 24 8 */
dma_addr_t rx_dma; /* 32 8 */
struct sg_table tx_sg; /* 40 16 */
struct sg_table rx_sg; /* 56 16 */
/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
unsigned int dummy_data:1; /* 72: 0 4 */
unsigned int cs_off:1; /* 72: 1 4 */
unsigned int cs_change:1; /* 72: 2 4 */
unsigned int tx_nbits:3; /* 72: 3 4 */
unsigned int rx_nbits:3; /* 72: 6 4 */
/* XXX 7 bits hole, try to pack */
/* Bitfield combined with next fields */
u8 bits_per_word; /* 74 1 */
/* XXX 1 byte hole, try to pack */
struct spi_delay delay; /* 76 4 */
/* XXX last struct has 1 byte of padding */
struct spi_delay cs_change_delay; /* 80 4 */
/* XXX last struct has 1 byte of padding */
struct spi_delay word_delay; /* 84 4 */
/* XXX last struct has 1 byte of padding */
u32 speed_hz; /* 88 4 */
u32 effective_speed_hz; /* 92 4 */
unsigned int ptp_sts_word_pre; /* 96 4 */
unsigned int ptp_sts_word_post; /* 100 4 */
struct ptp_system_timestamp * ptp_sts; /* 104 8 */
bool timestamped; /* 112 1 */
/* XXX 7 bytes hole, try to pack */
struct list_head transfer_list; /* 120 16 */
/* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
u16 error; /* 136 2 */
/* size: 144, cachelines: 3, members: 24 */
/* sum members: 124, holes: 3, sum holes: 12 */
/* sum bitfield members: 9 bits, bit holes: 1, sum bit holes: 7 bits */
/* padding: 6 */
/* paddings: 3, sum paddings: 3 */
/* last cacheline: 16 bytes */
};
After:
=====
struct spi_transfer {
const void * tx_buf; /* 0 8 */
void * rx_buf; /* 8 8 */
unsigned int len; /* 16 4 */
u16 error; /* 20 2 */
/* XXX 2 bytes hole, try to pack */
dma_addr_t tx_dma; /* 24 8 */
dma_addr_t rx_dma; /* 32 8 */
struct sg_table tx_sg; /* 40 16 */
struct sg_table rx_sg; /* 56 16 */
/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
unsigned int dummy_data:1; /* 72: 0 4 */
unsigned int cs_off:1; /* 72: 1 4 */
unsigned int cs_change:1; /* 72: 2 4 */
unsigned int tx_nbits:3; /* 72: 3 4 */
unsigned int rx_nbits:3; /* 72: 6 4 */
unsigned int timestamped:1; /* 72: 9 4 */
/* XXX 6 bits hole, try to pack */
/* Bitfield combined with next fields */
u8 bits_per_word; /* 74 1 */
/* XXX 1 byte hole, try to pack */
struct spi_delay delay; /* 76 4 */
/* XXX last struct has 1 byte of padding */
struct spi_delay cs_change_delay; /* 80 4 */
/* XXX last struct has 1 byte of padding */
struct spi_delay word_delay; /* 84 4 */
/* XXX last struct has 1 byte of padding */
u32 speed_hz; /* 88 4 */
u32 effective_speed_hz; /* 92 4 */
unsigned int ptp_sts_word_pre; /* 96 4 */
unsigned int ptp_sts_word_post; /* 100 4 */
struct ptp_system_timestamp * ptp_sts; /* 104 8 */
struct list_head transfer_list; /* 112 16 */
/* size: 128, cachelines: 2, members: 24 */
/* sum members: 123, holes: 2, sum holes: 3 */
/* sum bitfield members: 10 bits, bit holes: 1, sum bit holes: 6 bits */
/* paddings: 3, sum paddings: 3 */
};
---
drivers/spi/spi.c | 2 +-
include/linux/spi/spi.h | 9 ++++-----
2 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 9f5c6b9f5135..44b85a8d47f1 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1927,7 +1927,7 @@ void spi_take_timestamp_post(struct spi_controller *ctlr,
/* Capture the resolution of the timestamp */
xfer->ptp_sts_word_post = progress;
- xfer->timestamped = true;
+ xfer->timestamped = 1;
}
EXPORT_SYMBOL_GPL(spi_take_timestamp_post);
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 988aabc31871..4fa26b9a3572 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -1022,6 +1022,9 @@ struct spi_transfer {
void *rx_buf;
unsigned len;
+#define SPI_TRANS_FAIL_NO_START BIT(0)
+ u16 error;
+
dma_addr_t tx_dma;
dma_addr_t rx_dma;
struct sg_table tx_sg;
@@ -1032,6 +1035,7 @@ struct spi_transfer {
unsigned cs_change:1;
unsigned tx_nbits:3;
unsigned rx_nbits:3;
+ unsigned timestamped:1;
#define SPI_NBITS_SINGLE 0x01 /* 1bit transfer */
#define SPI_NBITS_DUAL 0x02 /* 2bits transfer */
#define SPI_NBITS_QUAD 0x04 /* 4bits transfer */
@@ -1048,12 +1052,7 @@ struct spi_transfer {
struct ptp_system_timestamp *ptp_sts;
- bool timestamped;
-
struct list_head transfer_list;
-
-#define SPI_TRANS_FAIL_NO_START BIT(0)
- u16 error;
};
/**
--
2.34.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] spi: Reorder fields in 'struct spi_transfer'
2023-02-14 10:34 [PATCH] spi: Reorder fields in 'struct spi_transfer' Christophe JAILLET
@ 2023-02-14 21:10 ` Mark Brown
0 siblings, 0 replies; 2+ messages in thread
From: Mark Brown @ 2023-02-14 21:10 UTC (permalink / raw)
To: Richard Cochran, Christophe JAILLET
Cc: linux-kernel, kernel-janitors, linux-spi, netdev
On Tue, 14 Feb 2023 11:34:50 +0100, Christophe JAILLET wrote:
> Group some variables based on their sizes to reduce hole and avoid padding.
> On x86_64, this shrinks the size from 144 to 128 bytes.
>
> Turn 'timestamped' into a bitfield so that it can be easily merged with
> some other bifields and move 'error'.
>
> This should have no real impact on memory allocation because 'struct
> spi_transfer' is mostly used on stack, but it can save a few cycles
> when the structure is initialized or copied.
>
> [...]
Applied to
broonie/spi.git for-next
Thanks!
[1/1] spi: Reorder fields in 'struct spi_transfer'
commit: 9d77522b45246c3dc5950b9641aea49ce3c973d7
All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.
You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.
If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.
Please add any relevant lists and maintainers to the CCs when replying
to this mail.
Thanks,
Mark
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