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Message-ID: <1289891544.3364.193.camel@edumazet-laptop>
Date: Tue, 16 Nov 2010 08:12:24 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next-2.6] net: reorder struct sock fields
Right now, fields in struct sock are not optimally ordered, because each
path (RX softirq, TX completion, RX user, TX user) has to touch fields
that are contained in many different cache lines.
The really critical thing is to shrink number of cache lines that are
used at RX softirq time : CPU handling softirqs for a device can receive
many frames per second for many sockets. If load is too big, we can drop
frames at NIC level. RPS or multiqueue cards can help, but better reduce
latency if possible.
This patch starts with UDP protocol, then additional patches will try to
reduce latencies of other ones as well.
At RX softirq time, fields of interest for UDP protocol are :
(not counting ones in inet struct for the lookup)
Read/Written:
sk_refcnt (atomic increment/decrement)
sk_rmem_alloc & sk_backlog.len (to check if there is room in queues)
sk_receive_queue
sk_backlog (if socket locked by user program)
sk_rxhash
sk_forward_alloc
Read only:
sk_rcvbuf (sk_rcvqueues_full())
sk_filter
sk_wq
Additional notes :
- sk_backlog has one hole on 64bit arches. We can fill it to save 8
bytes.
- sk_backlog is used only if RX sofirq handler finds the socket while
locked by user.
- sk_rxhash is written only once per flow.
Final layout :
1) One section grouping all read/write fields, but placing rxhash and
sk_backlog at the end of this section.
2) One section grouping all read fields in RX handler
(sk_filter, sk_rcv_buf, sk_wq)
3) Section used by other paths
I'll post a patch on its own to put sk_refcnt in the same cache line
than section [1] (or at least, at the end of struct sock_common)
New offsets on 64bit arch :
sizeof(struct sock)=0x268
offsetof(struct sock, sk_refcnt) =0x10
offsetof(struct sock, sk_lock) =0x48
offsetof(struct sock, sk_receive_queue)=0x68
offsetof(struct sock, sk_backlog)=0x80
offsetof(struct sock, sk_rmem_alloc)=0x80
offsetof(struct sock, sk_forward_alloc)=0x98
offsetof(struct sock, sk_rxhash)=0x9c
offsetof(struct sock, sk_rcvbuf)=0xac
offsetof(struct sock, sk_filter)=0xa0
offsetof(struct sock, sk_wq)=0xb0
Instead of :
sizeof(struct sock)=0x270
offsetof(struct sock, sk_refcnt) =0x10
offsetof(struct sock, sk_lock) =0x50
offsetof(struct sock, sk_receive_queue)=0x178
offsetof(struct sock, sk_backlog)=0xf8
offsetof(struct sock, sk_rmem_alloc)=0x168
offsetof(struct sock, sk_forward_alloc)=0x26c
offsetof(struct sock, sk_rxhash)=0x288
offsetof(struct sock, sk_rcvbuf)=0x4c
offsetof(struct sock, sk_filter)=0x368
offsetof(struct sock, sk_wq)=0x110
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
include/net/sock.h | 49 ++++++++++++++++++++++++-------------------
1 file changed, 28 insertions(+), 21 deletions(-)
diff --git a/include/net/sock.h b/include/net/sock.h
index a6338d0..7742572 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -241,51 +241,59 @@ struct sock {
#define sk_bind_node __sk_common.skc_bind_node
#define sk_prot __sk_common.skc_prot
#define sk_net __sk_common.skc_net
- kmemcheck_bitfield_begin(flags);
- unsigned int sk_shutdown : 2,
- sk_no_check : 2,
- sk_userlocks : 4,
- sk_protocol : 8,
- sk_type : 16;
- kmemcheck_bitfield_end(flags);
- int sk_rcvbuf;
socket_lock_t sk_lock;
+ struct sk_buff_head sk_receive_queue;
/*
* The backlog queue is special, it is always used with
* the per-socket spinlock held and requires low latency
* access. Therefore we special case it's implementation.
+ * Note : rmem_alloc is in this structure to fill a hole
+ * on 64bit arches, not because its logically part of
+ * backlog.
*/
struct {
- struct sk_buff *head;
- struct sk_buff *tail;
- int len;
+ atomic_t rmem_alloc;
+ int len;
+ struct sk_buff *head;
+ struct sk_buff *tail;
} sk_backlog;
+#define sk_rmem_alloc sk_backlog.rmem_alloc
+ int sk_forward_alloc;
+#ifdef CONFIG_RPS
+ __u32 sk_rxhash;
+#endif
+ struct sk_filter __rcu *sk_filter;
+ kmemcheck_bitfield_begin(flags);
+ unsigned int sk_shutdown : 2,
+ sk_no_check : 2,
+ sk_userlocks : 4,
+ sk_protocol : 8,
+ sk_type : 16;
+ kmemcheck_bitfield_end(flags);
+ int sk_rcvbuf;
+
struct socket_wq *sk_wq;
+
+#ifdef CONFIG_NET_DMA
+ struct sk_buff_head sk_async_wait_queue;
+#endif
+
struct dst_entry *sk_dst_cache;
#ifdef CONFIG_XFRM
struct xfrm_policy *sk_policy[2];
#endif
spinlock_t sk_dst_lock;
- atomic_t sk_rmem_alloc;
atomic_t sk_wmem_alloc;
atomic_t sk_omem_alloc;
int sk_sndbuf;
- struct sk_buff_head sk_receive_queue;
struct sk_buff_head sk_write_queue;
-#ifdef CONFIG_NET_DMA
- struct sk_buff_head sk_async_wait_queue;
-#endif
int sk_wmem_queued;
- int sk_forward_alloc;
gfp_t sk_allocation;
int sk_route_caps;
int sk_route_nocaps;
int sk_gso_type;
unsigned int sk_gso_max_size;
int sk_rcvlowat;
-#ifdef CONFIG_RPS
- __u32 sk_rxhash;
-#endif
unsigned long sk_flags;
unsigned long sk_lingertime;
struct sk_buff_head sk_error_queue;
@@ -301,7 +309,6 @@ struct sock {
const struct cred *sk_peer_cred;
long sk_rcvtimeo;
long sk_sndtimeo;
- struct sk_filter __rcu *sk_filter;
void *sk_protinfo;
struct timer_list sk_timer;
ktime_t sk_stamp;
--
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