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netfilter: x_tables: align per cpu xt_counter
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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>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Eric Dumazet authored and Pablo Neira Ayuso committed Jun 18, 2015
1 parent 01555e7 commit a1a56aa
Showing 1 changed file with 4 additions and 2 deletions.
6 changes: 4 additions & 2 deletions include/linux/netfilter/x_tables.h
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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;
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