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Message-Id: <93a051da85a895bc6003aedfb00a13e1c2fc6338.1676370870.git.christophe.jaillet@wanadoo.fr>
Date: Tue, 14 Feb 2023 11:34:50 +0100
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Mark Brown <broonie@...nel.org>,
Richard Cochran <richardcochran@...il.com>
Cc: linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
Christophe JAILLET <christophe.jaillet@...adoo.fr>,
linux-spi@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH] spi: Reorder fields in 'struct spi_transfer'
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@...adoo.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
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