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Message-ID: <7c8ec848-4a78-4015-b7ff-9067c1fd3bba@hartkopp.net>
Date: Mon, 15 Sep 2025 19:42:30 +0200
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Vincent Mailhol <mailhol@...nel.org>,
Marc Kleine-Budde <mkl@...gutronix.de>
Cc: linux-can@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] can: raw: reorder struct raw_sock's members to
optimise packing
On 15.09.25 11:23, Vincent Mailhol wrote:
> 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>
Acked-by: Oliver Hartkopp <socketcan@...tkopp.net>
> ---
> 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;
> };
>
>
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