netdev - [PATCH net-next] net: reorder flowi

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Date:   Wed, 28 Nov 2018 17:37:53 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>
Subject: [PATCH net-next] net: reorder flowi_common fields to avoid holes

the flowi* structures are used and memsetted by server functions
in critical path. Currently flowi_common has a couple of holes that
we can eliminate reordering the struct fields. As a side effect,
both flowi4 and flowi6 shrink by 8 bytes.

Before:
pahole -EC flowi_common
struct flowi_common {
// ...
	/* size: 40, cachelines: 1, members: 10 */
	/* sum members: 32, holes: 1, sum holes: 4 */
	/* padding: 4 */
	/* last cacheline: 40 bytes */
};
pahole -EC flowi6
struct flowi6 {
// ...
        /* size: 88, cachelines: 2, members: 6 */
        /* padding: 4 */
        /* last cacheline: 24 bytes */
};
pahole -EC flowi4
struct flowi4 {
// ...
        /* size: 56, cachelines: 1, members: 4 */
        /* padding: 4 */
        /* last cacheline: 56 bytes */
};

After:
struct flowi_common {
// ...
	/* size: 32, cachelines: 1, members: 10 */
	/* last cacheline: 32 bytes */
};
struct flowi6 {
// ...
        /* size: 80, cachelines: 2, members: 6 */
        /* padding: 4 */
        /* last cacheline: 16 bytes */
};
struct flowi4 {
// ...
        /* size: 48, cachelines: 1, members: 4 */
        /* padding: 4 */
        /* last cacheline: 48 bytes */
};

Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 include/net/flow.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/flow.h b/include/net/flow.h
index 8ce21793094e..93f2c9a0f098 100644
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -38,8 +38,8 @@ struct flowi_common {
 #define FLOWI_FLAG_KNOWN_NH		0x02
 #define FLOWI_FLAG_SKIP_NH_OIF		0x04
 	__u32	flowic_secid;
-	struct flowi_tunnel flowic_tun_key;
 	kuid_t  flowic_uid;
+	struct flowi_tunnel flowic_tun_key;
 };
 
 union flowi_uli {
-- 
2.19.2