| Message ID | 393ad1a5aef0aa28d839eeb3d7477da0e0eeb0b0.1687080803.git.christophe.jaillet@wanadoo.fr (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 066768b7305b1524d261fdc543d25fd60d955254 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next] mctp: Reorder fields in 'struct mctp_route' | expand |
On Sun, Jun 18, 2023 at 11:33:55AM +0200, Christophe JAILLET wrote: > Group some variables based on their sizes to reduce hole and avoid padding. > On x86_64, this shrinks the size of 'struct mctp_route' > from 72 to 64 bytes. > > It saves a few bytes of memory and is more cache-line friendly. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> Reviewed-by: Simon Horman <simon.horman@corigine.com>
Hi Christoph, > Group some variables based on their sizes to reduce hole and avoid > padding. On x86_64, this shrinks the size of 'struct mctp_route' from > 72 to 64 bytes. > > It saves a few bytes of memory and is more cache-line friendly. The savings will be fairly minimal, but this doesn't affect readability for the route struct. LGTM. Acked-by: Jeremy Kerr <jk@codeconstruct.com.au> Thanks! Jeremy
Sun, Jun 18, 2023 at 11:33:55AM CEST, christophe.jaillet@wanadoo.fr wrote: >Group some variables based on their sizes to reduce hole and avoid padding. >On x86_64, this shrinks the size of 'struct mctp_route' >from 72 to 64 bytes. > >It saves a few bytes of memory and is more cache-line friendly. > >Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Hello: This patch was applied to netdev/net-next.git (main) by Jakub Kicinski <kuba@kernel.org>: On Sun, 18 Jun 2023 11:33:55 +0200 you wrote: > Group some variables based on their sizes to reduce hole and avoid padding. > On x86_64, this shrinks the size of 'struct mctp_route' > from 72 to 64 bytes. > > It saves a few bytes of memory and is more cache-line friendly. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > > [...] Here is the summary with links: - [net-next] mctp: Reorder fields in 'struct mctp_route' https://git.kernel.org/netdev/net-next/c/066768b7305b You are awesome, thank you!
diff --git a/include/net/mctp.h b/include/net/mctp.h index 82800d521c3d..da86e106c91d 100644 --- a/include/net/mctp.h +++ b/include/net/mctp.h @@ -234,9 +234,9 @@ struct mctp_flow { struct mctp_route { mctp_eid_t min, max; - struct mctp_dev *dev; - unsigned int mtu; unsigned char type; + unsigned int mtu; + struct mctp_dev *dev; int (*output)(struct mctp_route *route, struct sk_buff *skb);
Group some variables based on their sizes to reduce hole and avoid padding. On x86_64, this shrinks the size of 'struct mctp_route' from 72 to 64 bytes. It saves a few bytes of memory and is more cache-line friendly. Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> --- Using pahole Before: ====== struct mctp_route { mctp_eid_t min; /* 0 1 */ mctp_eid_t max; /* 1 1 */ /* XXX 6 bytes hole, try to pack */ struct mctp_dev * dev; /* 8 8 */ unsigned int mtu; /* 16 4 */ unsigned char type; /* 20 1 */ /* XXX 3 bytes hole, try to pack */ int (*output)(struct mctp_route *, struct sk_buff *); /* 24 8 */ struct list_head list; /* 32 16 */ refcount_t refs; /* 48 4 */ /* XXX 4 bytes hole, try to pack */ struct callback_head rcu __attribute__((__aligned__(8))); /* 56 16 */ /* size: 72, cachelines: 2, members: 9 */ /* sum members: 59, holes: 3, sum holes: 13 */ /* forced alignments: 1, forced holes: 1, sum forced holes: 4 */ /* last cacheline: 8 bytes */ } __attribute__((__aligned__(8))); After: ===== struct mctp_route { mctp_eid_t min; /* 0 1 */ mctp_eid_t max; /* 1 1 */ unsigned char type; /* 2 1 */ /* XXX 1 byte hole, try to pack */ unsigned int mtu; /* 4 4 */ struct mctp_dev * dev; /* 8 8 */ int (*output)(struct mctp_route *, struct sk_buff *); /* 16 8 */ struct list_head list; /* 24 16 */ refcount_t refs; /* 40 4 */ /* XXX 4 bytes hole, try to pack */ struct callback_head rcu __attribute__((__aligned__(8))); /* 48 16 */ /* size: 64, cachelines: 1, members: 9 */ /* sum members: 59, holes: 2, sum holes: 5 */ /* forced alignments: 1, forced holes: 1, sum forced holes: 4 */ } __attribute__((__aligned__(8))); --- include/net/mctp.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)