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Message-Id: <20250915-can-raw-repack-v1-3-5ea293bc6d33@kernel.org>
Date: Mon, 15 Sep 2025 18:23:15 +0900
From: Vincent Mailhol <mailhol@...nel.org>
To: Oliver Hartkopp <socketcan@...tkopp.net>,
Marc Kleine-Budde <mkl@...gutronix.de>
Cc: linux-can@...r.kernel.org, linux-kernel@...r.kernel.org,
Vincent Mailhol <mailhol@...nel.org>
Subject: [PATCH 3/3] can: raw: reorder struct raw_sock's members to
optimise packing
struct raw_sock has several holes. Reorder the fields to save 8 bytes.
Statistics before:
$ pahole --class_name=raw_sock net/can/raw.o
struct raw_sock {
struct sock sk __attribute__((__aligned__(8))); /* 0 776 */
/* XXX last struct has 1 bit hole */
/* --- cacheline 12 boundary (768 bytes) was 8 bytes ago --- */
int bound; /* 776 4 */
int ifindex; /* 780 4 */
struct net_device * dev; /* 784 8 */
netdevice_tracker dev_tracker; /* 792 0 */
struct list_head notifier; /* 792 16 */
unsigned int loopback:1; /* 808: 0 4 */
unsigned int recv_own_msgs:1; /* 808: 1 4 */
unsigned int fd_frames:1; /* 808: 2 4 */
unsigned int xl_frames:1; /* 808: 3 4 */
/* XXX 4 bits hole, try to pack */
/* Bitfield combined with next fields */
struct can_raw_vcid_options raw_vcid_opts; /* 809 4 */
/* XXX 3 bytes hole, try to pack */
canid_t tx_vcid_shifted; /* 816 4 */
canid_t rx_vcid_shifted; /* 820 4 */
canid_t rx_vcid_mask_shifted; /* 824 4 */
int join_filters; /* 828 4 */
/* --- cacheline 13 boundary (832 bytes) --- */
int count; /* 832 4 */
struct can_filter dfilter; /* 836 8 */
/* XXX 4 bytes hole, try to pack */
struct can_filter * filter; /* 848 8 */
can_err_mask_t err_mask; /* 856 4 */
/* XXX 4 bytes hole, try to pack */
struct uniqframe * uniq; /* 864 8 */
/* size: 872, cachelines: 14, members: 20 */
/* sum members: 860, holes: 3, sum holes: 11 */
/* sum bitfield members: 4 bits, bit holes: 1, sum bit holes: 4 bits */
/* member types with bit holes: 1, total: 1 */
/* forced alignments: 1 */
/* last cacheline: 40 bytes */
} __attribute__((__aligned__(8)));
...and after:
$ pahole --class_name=raw_sock net/can/raw.o
struct raw_sock {
struct sock sk __attribute__((__aligned__(8))); /* 0 776 */
/* XXX last struct has 1 bit hole */
/* --- cacheline 12 boundary (768 bytes) was 8 bytes ago --- */
int bound; /* 776 4 */
int ifindex; /* 780 4 */
struct net_device * dev; /* 784 8 */
netdevice_tracker dev_tracker; /* 792 0 */
struct list_head notifier; /* 792 16 */
struct can_raw_vcid_options raw_vcid_opts; /* 808 4 */
unsigned int loopback:1; /* 812: 0 4 */
unsigned int recv_own_msgs:1; /* 812: 1 4 */
unsigned int fd_frames:1; /* 812: 2 4 */
unsigned int xl_frames:1; /* 812: 3 4 */
/* XXX 28 bits hole, try to pack */
canid_t tx_vcid_shifted; /* 816 4 */
canid_t rx_vcid_shifted; /* 820 4 */
canid_t rx_vcid_mask_shifted; /* 824 4 */
can_err_mask_t err_mask; /* 828 4 */
/* --- cacheline 13 boundary (832 bytes) --- */
int join_filters; /* 832 4 */
int count; /* 836 4 */
struct can_filter dfilter; /* 840 8 */
struct can_filter * filter; /* 848 8 */
struct uniqframe * uniq; /* 856 8 */
/* size: 864, cachelines: 14, members: 20 */
/* sum members: 860 */
/* sum bitfield members: 4 bits, bit holes: 1, sum bit holes: 28 bits */
/* member types with bit holes: 1, total: 1 */
/* forced alignments: 1 */
/* last cacheline: 32 bytes */
} __attribute__((__aligned__(8)));
Signed-off-by: Vincent Mailhol <mailhol@...nel.org>
---
net/can/raw.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/can/raw.c b/net/can/raw.c
index cec580ecd58e36931d1be05716e6beb9c93aa271..81f5de63bcfaacf3f51670159fb3d1d7d1fc6020 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -87,19 +87,19 @@ struct raw_sock {
struct net_device *dev;
netdevice_tracker dev_tracker;
struct list_head notifier;
+ struct can_raw_vcid_options raw_vcid_opts;
unsigned int loopback:1;
unsigned int recv_own_msgs:1;
unsigned int fd_frames:1;
unsigned int xl_frames:1;
- struct can_raw_vcid_options raw_vcid_opts;
canid_t tx_vcid_shifted;
canid_t rx_vcid_shifted;
canid_t rx_vcid_mask_shifted;
+ can_err_mask_t err_mask;
int join_filters;
int count; /* number of active filters */
struct can_filter dfilter; /* default/single filter */
struct can_filter *filter; /* pointer to filter(s) */
- can_err_mask_t err_mask;
struct uniqframe __percpu *uniq;
};
--
2.49.1
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