[PATCH net-next] x_table: align per cpu xt_counter

[PATCH net-next] x_table: align per cpu xt_counter

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Let's force a 16 bytes alignment on xt_counter percpu allocations,
so that bytes and packets sit in same cache line.

xt_counter being exported to user space, we cannot add __align(16) on
the structure itself.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
---
 include/linux/netfilter/x_tables.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 95693c4cebdda473a2f3e427dcc2511e83bf7405..1c97a2204379e14676ee33f0b15c5174b7afe680 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -356,7 +356,8 @@ static inline unsigned long ifname_compare_aligned(const char *_a,
  * so nothing needs to be done there.
  *
  * xt_percpu_counter_alloc returns the address of the percpu
- * counter, or 0 on !SMP.
+ * counter, or 0 on !SMP. We force an alignment of 16 bytes
+ * so that bytes/packets share a common cache line.
  *
  * Hence caller must use IS_ERR_VALUE to check for error, this
  * allows us to return 0 for single core systems without forcing
@@ -365,7 +366,8 @@ static inline unsigned long ifname_compare_aligned(const char *_a,
 static inline u64 xt_percpu_counter_alloc(void)
 {
 	if (nr_cpu_ids > 1) {
-		void __percpu *res = alloc_percpu(struct xt_counters);
+		void __percpu *res = __alloc_percpu(sizeof(struct xt_counters),
+						    sizeof(struct xt_counters));
 
 		if (res == NULL)
 			return (u64) -ENOMEM;

Re: [PATCH net-next] x_table: align per cpu xt_counter

[Florian Westphal]

Eric Dumazet <eric.dumazet@gmail.com> wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Let's force a 16 bytes alignment on xt_counter percpu allocations,
> so that bytes and packets sit in same cache line.
> 
> xt_counter being exported to user space, we cannot add __align(16) on
> the structure itself.

Sorry, I was away.  Looks great.

Acked-by: Florian Westphal <fw@strlen.de>

Re: [PATCH net-next] x_table: align per cpu xt_counter

[Pablo Neira Ayuso]

On Wed, Jun 17, 2015 at 07:08:15PM +0200, Florian Westphal wrote:
> Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > Let's force a 16 bytes alignment on xt_counter percpu allocations,
> > so that bytes and packets sit in same cache line.
> > 
> > xt_counter being exported to user space, we cannot add __align(16) on
> > the structure itself.
> 
> Sorry, I was away.  Looks great.
> 
> Acked-by: Florian Westphal <fw@strlen.de>

Applied, thanks Eric and Florian !

Re: [PATCH net-next] x_table: align per cpu xt_counter

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 15 Jun 2015 18:10:13 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> Let's force a 16 bytes alignment on xt_counter percpu allocations,
> so that bytes and packets sit in same cache line.
> 
> xt_counter being exported to user space, we cannot add __align(16) on
> the structure itself.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Florian Westphal <fw@strlen.de>

Pablo, I assume you will take this.

Re: [PATCH net-next] x_table: align per cpu xt_counter

[Pablo Neira Ayuso]

On Thu, Jun 18, 2015 at 03:43:26AM -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Mon, 15 Jun 2015 18:10:13 -0700
> 
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > Let's force a 16 bytes alignment on xt_counter percpu allocations,
> > so that bytes and packets sit in same cache line.
> > 
> > xt_counter being exported to user space, we cannot add __align(16) on
> > the structure itself.
> > 
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Cc: Florian Westphal <fw@strlen.de>
> 
> Pablo, I assume you will take this.

Yes, I'll prepare another pull request for you along today.