packet: reorder a member in packet_ring_buffer

There's a 4 byte hole in packet_ring_buffer structure before
prb_bdqc, that can be filled with 'pending' member, thus we can
reduce the overall structure size from 224 bytes to 216 bytes.
This also has the side-effect, that in struct packet_sock 2*4 byte
holes after the embedded packet_ring_buffer members are removed,
and overall, packet_sock can be reduced by 1 cacheline:

Before: size: 1344, cachelines: 21, members: 24
After:  size: 1280, cachelines: 20, members: 24

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/packet/internal.h b/net/packet/internal.h
index e891f025a1b9870f35fb72f341d7f8f3f993e476..650751b9a7ee9c3f92382f37f3a5339562a4c733 100644 (file)
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -54,6 +54,7 @@ struct pgv {
 
 struct packet_ring_buffer {
        struct pgv              *pg_vec;
+
        unsigned int            head;
        unsigned int            frames_per_block;
        unsigned int            frame_size;
@@ -63,8 +64,9 @@ struct packet_ring_buffer {
        unsigned int            pg_vec_pages;
        unsigned int            pg_vec_len;
 
-       struct tpacket_kbdq_core        prb_bdqc;
        atomic_t                pending;
+
+       struct tpacket_kbdq_core        prb_bdqc;
 };
 
 extern struct mutex fanout_mutex;