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inet: shrink inet_timewait_death_row by 48 bytes 

struct inet_timewait_death_row uses two cache lines, because we want
tw_count to use a full cache line to avoid false sharing.

Rework its definition and placement in netns_ipv4 so that:

1) We add 60 bytes of padding after tw_count to avoid
  false sharing, knowing that tcp_death_row will
  have ____cacheline_aligned_in_smp attribute.

2) We do not risk padding before tcp_death_row, because
  we move it at the beginning of netns_ipv4, even if new
 fields are added later.

3) We do not waste 48 bytes of padding after it.

Note that I have not changed dccp.

pahole result for struct netns_ipv4 before/after the patch :

/* size: 832, cachelines: 13, members: 139 */
/* sum members: 721, holes: 12, sum holes: 95 */
/* padding: 16 */
/* paddings: 2, sum paddings: 55 */

->

/* size: 768, cachelines: 12, members: 139 */
/* sum members: 673, holes: 11, sum holes: 39 */
/* padding: 56 */
/* paddings: 2, sum paddings: 7 */
/* forced alignments: 1 */

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-03-31 10:52:05 -07:00 committed by David S. Miller
parent 30b8817f5f
commit 1caf8d39c5
1 changed files with 5 additions and 2 deletions
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7
include/net/netns/ipv4.h
View File

@ -32,14 +32,18 @@ struct inet_hashinfo;
struct inet_timewait_death_row {
atomic_t tw_count;
char tw_pad[L1_CACHE_BYTES - sizeof(atomic_t)];
struct inet_hashinfo *hashinfo ____cacheline_aligned_in_smp;
struct inet_hashinfo *hashinfo;
int sysctl_max_tw_buckets;
};
struct tcp_fastopen_context;
struct netns_ipv4 {
/* Please keep tcp_death_row at first field in netns_ipv4 */
struct inet_timewait_death_row tcp_death_row ____cacheline_aligned_in_smp;
#ifdef CONFIG_SYSCTL
struct ctl_table_header *forw_hdr;
struct ctl_table_header *frags_hdr;
@ -175,7 +179,6 @@ struct netns_ipv4 {
int sysctl_tcp_comp_sack_nr;
unsigned long sysctl_tcp_comp_sack_delay_ns;
unsigned long sysctl_tcp_comp_sack_slack_ns;
struct inet_timewait_death_row tcp_death_row;
int sysctl_max_syn_backlog;
int sysctl_tcp_fastopen;
const struct tcp_congestion_ops __rcu *tcp_congestion_control;