From: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
To: Jeremy Kerr <jk@codeconstruct.com.au>,
Matt Johnston <matt@codeconstruct.com.au>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>
Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org,
Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
netdev@vger.kernel.org
Subject: [PATCH net-next] mctp: Reorder fields in 'struct mctp_route'
Date: Sun, 18 Jun 2023 11:33:55 +0200 [thread overview]
Message-ID: <393ad1a5aef0aa28d839eeb3d7477da0e0eeb0b0.1687080803.git.christophe.jaillet@wanadoo.fr> (raw)
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(-)
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);
--
2.34.1
next reply other threads:[~2023-06-18 9:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-18 9:33 Christophe JAILLET [this message]
2023-06-19 14:04 ` [PATCH net-next] mctp: Reorder fields in 'struct mctp_route' Simon Horman
2023-06-19 14:06 ` Jeremy Kerr
2023-06-19 14:41 ` Jiri Pirko
2023-06-21 3:40 ` patchwork-bot+netdevbpf
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