[PATCH v2 3/3] can: raw: reorder struct raw_sock's members to optimise packing

[Vincent Mailhol <mailhol@kernel.org>]

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                        ifindex;              /*   776     4 */

  	/* XXX 4 bytes hole, try to pack */

  	struct net_device *        dev;                  /*   784     8 */
  	netdevice_tracker          dev_tracker;          /*   792     0 */
  	struct list_head           notifier;             /*   792    16 */
  	unsigned int               bound:1;              /*   808: 0  4 */
  	unsigned int               loopback:1;           /*   808: 1  4 */
  	unsigned int               recv_own_msgs:1;      /*   808: 2  4 */
  	unsigned int               fd_frames:1;          /*   808: 3  4 */
  	unsigned int               xl_frames:1;          /*   808: 4  4 */
  	unsigned int               join_filters:1;       /*   808: 5  4 */

  	/* XXX 2 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                        count;                /*   828     4 */
  	/* --- cacheline 13 boundary (832 bytes) --- */
  	struct can_filter          dfilter;              /*   832     8 */
  	struct can_filter *        filter;               /*   840     8 */
  	can_err_mask_t             err_mask;             /*   848     4 */

  	/* XXX 4 bytes hole, try to pack */

  	struct uniqframe *         uniq;                 /*   856     8 */

  	/* size: 864, cachelines: 14, members: 20 */
  	/* sum members: 852, holes: 3, sum holes: 11 */
  	/* sum bitfield members: 6 bits, bit holes: 1, sum bit holes: 2 bits */
  	/* member types with bit holes: 1, total: 1 */
  	/* forced alignments: 1 */
  	/* last cacheline: 32 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 --- */
  	struct net_device *        dev;                  /*   776     8 */
  	netdevice_tracker          dev_tracker;          /*   784     0 */
  	struct list_head           notifier;             /*   784    16 */
  	int                        ifindex;              /*   800     4 */
  	unsigned int               bound:1;              /*   804: 0  4 */
  	unsigned int               loopback:1;           /*   804: 1  4 */
  	unsigned int               recv_own_msgs:1;      /*   804: 2  4 */
  	unsigned int               fd_frames:1;          /*   804: 3  4 */
  	unsigned int               xl_frames:1;          /*   804: 4  4 */
  	unsigned int               join_filters:1;       /*   804: 5  4 */

  	/* XXX 2 bits hole, try to pack */
  	/* Bitfield combined with next fields */

  	struct can_raw_vcid_options raw_vcid_opts;       /*   805     4 */

  	/* XXX 3 bytes hole, try to pack */

  	canid_t                    tx_vcid_shifted;      /*   812     4 */
  	canid_t                    rx_vcid_shifted;      /*   816     4 */
  	canid_t                    rx_vcid_mask_shifted; /*   820     4 */
  	can_err_mask_t             err_mask;             /*   824     4 */
  	int                        count;                /*   828     4 */
  	/* --- cacheline 13 boundary (832 bytes) --- */
  	struct can_filter          dfilter;              /*   832     8 */
  	struct can_filter *        filter;               /*   840     8 */
  	struct uniqframe *         uniq;                 /*   848     8 */

  	/* size: 856, cachelines: 14, members: 20 */
  	/* sum members: 852, holes: 1, sum holes: 3 */
  	/* sum bitfield members: 6 bits, bit holes: 1, sum bit holes: 2 bits */
  	/* member types with bit holes: 1, total: 1 */
  	/* forced alignments: 1 */
  	/* last cacheline: 24 bytes */
  } __attribute__((__aligned__(8)));

Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Vincent Mailhol <mailhol@kernel.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 5a5ded519cd1768456c234c42dc4e865f7350dab..bf65d67b5df0135bf02d90c5e1070898a4f5592e 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -82,10 +82,10 @@ struct uniqframe {
 
 struct raw_sock {
 	struct sock sk;
-	int ifindex;
 	struct net_device *dev;
 	netdevice_tracker dev_tracker;
 	struct list_head notifier;
+	int ifindex;
 	unsigned int bound:1;
 	unsigned int loopback:1;
 	unsigned int recv_own_msgs:1;
@@ -96,10 +96,10 @@ struct raw_sock {
 	canid_t tx_vcid_shifted;
 	canid_t rx_vcid_shifted;
 	canid_t rx_vcid_mask_shifted;
+	can_err_mask_t err_mask;
 	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