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Date: Wed, 22 Aug 2007 19:06:10 -0300
From: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To: David Miller <davem@...emloft.net>
Cc: paul.moore@...com, tgraf@...g.ch, netdev@...r.kernel.org
Subject: Re: [RFC] Wild and crazy ideas involving struct sk_buff
Em Wed, Aug 22, 2007 at 02:36:27PM -0700, David Miller escreveu:
> From: Paul Moore <paul.moore@...com>
> Date: Wed, 22 Aug 2007 17:26:36 -0400
>
> > Was it just a thought, or was there some actual design/code/patchset
> > to go along with it that described the idea?
>
> It was a thought mentioned at the first two netconfs, but it
> went nowhere because the more we discussed the implementation
> the more horrific it began to sound :-)
Which makes it more interesting to make it work :-)
Anyway, there is space there to be used, in 32 and 64 bits we have two
bytes after queue_mapping (this kernel doesn't have CONFIG_NET_SCHED nor
CONFIG_NET_CLS_ACT enabled, if the first was we wouldn't have the hole,
but if both, as its common in distro kernels, were we would have the 2
bytes hole, as we can see on the pahole output for the 64bits kernel,
that uses the kernel config used in the Red Hat kernels.
Bonus points would go to continue the skb offset fight and reduce the
size of mac_header to two bytes, and then moving it to just after
queue_mapping. Do that and you'll get some credits :-P
- Arnaldo
[acme@...a net-2.6.24]$ pahole -C sk_buff ../32bits/net/core/skbuff.o
struct sk_buff {
struct sk_buff * next; /* 0 4 */
struct sk_buff * prev; /* 4 4 */
struct sock * sk; /* 8 4 */
ktime_t tstamp; /* 12 8 */
struct net_device * dev; /* 20 4 */
struct dst_entry * dst; /* 24 4 */
struct sec_path * sp; /* 28 4 */
char cb[48]; /* 32 48 */
/* --- cacheline 1 boundary (64 bytes) was 16 bytes ago --- */
unsigned int len; /* 80 4 */
unsigned int data_len; /* 84 4 */
__u16 mac_len; /* 88 2 */
__u16 hdr_len; /* 90 2 */
union {
__wsum csum; /* 4 */
struct {
__u16 csum_start; /* 92 2 */
__u16 csum_offset; /* 94 2 */
} /* 4 */
}; /* 92 4 */
__u32 priority; /* 96 4 */
__u8 local_df:1; /* 100 1 */
__u8 cloned:1; /* 100 1 */
__u8 ip_summed:2; /* 100 1 */
__u8 nohdr:1; /* 100 1 */
__u8 nfctinfo:3; /* 100 1 */
__u8 pkt_type:3; /* 101 1 */
__u8 fclone:2; /* 101 1 */
__u8 ipvs_property:1; /* 101 1 */
__u8 nf_trace:1; /* 101 1 */
/* XXX 1 bit hole, try to pack */
__be16 protocol; /* 102 2 */
void (*destructor)(struct sk_buff *); /* 104 4 */
int iif; /* 108 4 */
__u16 queue_mapping; /* 112 2 */
/* XXX 2 bytes hole, try to pack */
__u32 mark; /* 116 4 */
sk_buff_data_t transport_header; /* 120 4 */
sk_buff_data_t network_header; /* 124 4 */
/* --- cacheline 2 boundary (128 bytes) --- */
sk_buff_data_t mac_header; /* 128 4 */
sk_buff_data_t tail; /* 132 4 */
sk_buff_data_t end; /* 136 4 */
unsigned char * head; /* 140 4 */
unsigned char * data; /* 144 4 */
unsigned int truesize; /* 148 4 */
atomic_t users; /* 152 4 */
/* size: 156, cachelines: 3 */
/* sum members: 154, holes: 1, sum holes: 2 */
/* bit holes: 1, sum bit holes: 1 bits */
/* last cacheline: 28 bytes */
};
[acme@...a net-2.6.24]$ pahole -C sk_buff ../64bits/net/core/skbuff.o
struct sk_buff {
struct sk_buff * next; /* 0 8 */
struct sk_buff * prev; /* 8 8 */
struct sock * sk; /* 16 8 */
ktime_t tstamp; /* 24 8 */
struct net_device * dev; /* 32 8 */
struct dst_entry * dst; /* 40 8 */
struct sec_path * sp; /* 48 8 */
char cb[48]; /* 56 48 */
/* --- cacheline 1 boundary (64 bytes) was 40 bytes ago --- */
unsigned int len; /* 104 4 */
unsigned int data_len; /* 108 4 */
__u16 mac_len; /* 112 2 */
__u16 hdr_len; /* 114 2 */
union {
__wsum csum; /* 4 */
struct {
__u16 csum_start; /* 116 2 */
__u16 csum_offset; /* 118 2 */
} /* 4 */
}; /* 116 4 */
__u32 priority; /* 120 4 */
__u8 local_df:1; /* 124 1 */
__u8 cloned:1; /* 124 1 */
__u8 ip_summed:2; /* 124 1 */
__u8 nohdr:1; /* 124 1 */
__u8 nfctinfo:3; /* 124 1 */
__u8 pkt_type:3; /* 125 1 */
__u8 fclone:2; /* 125 1 */
__u8 ipvs_property:1; /* 125 1 */
__u8 nf_trace:1; /* 125 1 */
/* XXX 1 bit hole, try to pack */
__be16 protocol; /* 126 2 */
/* --- cacheline 2 boundary (128 bytes) --- */
void (*destructor)(struct sk_buff *); /* 128 8 */
struct nf_conntrack * nfct; /* 136 8 */
struct sk_buff * nfct_reasm; /* 144 8 */
struct nf_bridge_info * nf_bridge; /* 152 8 */
int iif; /* 160 4 */
__u16 queue_mapping; /* 164 2 */
__u16 tc_index; /* 166 2 */
__u16 tc_verd; /* 168 2 */
/* XXX 2 bytes hole, try to pack */
dma_cookie_t dma_cookie; /* 172 4 */
__u32 secmark; /* 176 4 */
__u32 mark; /* 180 4 */
sk_buff_data_t transport_header; /* 184 4 */
sk_buff_data_t network_header; /* 188 4 */
/* --- cacheline 3 boundary (192 bytes) --- */
sk_buff_data_t mac_header; /* 192 4 */
sk_buff_data_t tail; /* 196 4 */
sk_buff_data_t end; /* 200 4 */
/* XXX 4 bytes hole, try to pack */
unsigned char * head; /* 208 8 */
unsigned char * data; /* 216 8 */
unsigned int truesize; /* 224 4 */
atomic_t users; /* 228 4 */
/* size: 232, cachelines: 4 */
/* sum members: 226, holes: 2, sum holes: 6 */
/* bit holes: 1, sum bit holes: 1 bits */
/* last cacheline: 40 bytes */
};
-
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