* [PATCH] NET : align inet_protos[] on SMP
@ 2007-03-27 13:47 Eric Dumazet
2007-03-27 21:20 ` David Miller
0 siblings, 1 reply; 2+ messages in thread
From: Eric Dumazet @ 2007-03-27 13:47 UTC (permalink / raw)
To: David Miller; +Cc: netdev@vger.kernel.org
As IPPROTO_TCP is 6, it makes sense to make sure inet_protos[] array is properly cache line aligned to avoid false sharing on SMP.
c0680540 b peer_total
c0680544 b inet_peer_unused_head
c0680560 B inet_protos
On i386 this example, we can see that inet_protos[IPPROTO_TCP] shares a potentially hot (and modified) cache line.
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
diff --git a/net/ipv4/protocol.c b/net/ipv4/protocol.c
index da70fef..971ab93 100644
--- a/net/ipv4/protocol.c
+++ b/net/ipv4/protocol.c
@@ -45,7 +45,7 @@ #include <net/udp.h>
#include <net/ipip.h>
#include <linux/igmp.h>
-struct net_protocol *inet_protos[MAX_INET_PROTOS];
+struct net_protocol *inet_protos[MAX_INET_PROTOS] ____cacheline_aligned_in_smp;
static DEFINE_SPINLOCK(inet_proto_lock);
/*
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] NET : align inet_protos[] on SMP
2007-03-27 13:47 [PATCH] NET : align inet_protos[] on SMP Eric Dumazet
@ 2007-03-27 21:20 ` David Miller
0 siblings, 0 replies; 2+ messages in thread
From: David Miller @ 2007-03-27 21:20 UTC (permalink / raw)
To: dada1; +Cc: netdev
From: Eric Dumazet <dada1@cosmosbay.com>
Date: Tue, 27 Mar 2007 15:47:04 +0200
> As IPPROTO_TCP is 6, it makes sense to make sure inet_protos[] array is properly cache line aligned to avoid false sharing on SMP.
>
> c0680540 b peer_total
> c0680544 b inet_peer_unused_head
> c0680560 B inet_protos
>
> On i386 this example, we can see that inet_protos[IPPROTO_TCP] shares a potentially hot (and modified) cache line.
>
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Applied, thanks again Eric.
We could probably add some const markings to these things as well.
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2007-03-27 13:47 [PATCH] NET : align inet_protos[] on SMP Eric Dumazet
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