On Tue, 2015-08-25 at 13:24 +0530, Raghavendra K T wrote:
> Docker container creation linearly increased from around 1.6 sec to 7.5 sec
> (at 1000 containers) and perf data showed 50% ovehead in snmp_fold_field.
>
> reason: currently __snmp6_fill_stats64 calls snmp_fold_field that walks
> through per cpu data of an item (iteratively for around 90 items).
>
> idea: This patch tries to aggregate the statistics by going through
> all the items of each cpu sequentially which is reducing cache
> misses.
>
> Docker creation got faster by more than 2x after the patch.
>
> Result:
> Before After
> Docker creation time 6.836s 3.357s
> cache miss 2.7% 1.38%
>
> perf before:
> 50.73% docker [kernel.kallsyms] [k] snmp_fold_field
> 9.07% swapper [kernel.kallsyms] [k] snooze_loop
> 3.49% docker [kernel.kallsyms] [k] veth_stats_one
> 2.85% swapper [kernel.kallsyms] [k] _raw_spin_lock
>
> perf after:
> 10.56% swapper [kernel.kallsyms] [k] snooze_loop
> 8.72% docker [kernel.kallsyms] [k] snmp_get_cpu_field
> 7.59% docker [kernel.kallsyms] [k] veth_stats_one
> 3.65% swapper [kernel.kallsyms] [k] _raw_spin_lock
>
> Signed-off-by: Raghavendra K T <raghavendra...@linux.vnet.ibm.com>
> ---
> net/ipv6/addrconf.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 21c2c81..2ec905f 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -4624,16 +4624,24 @@ static inline void __snmp6_fill_statsdev(u64 *stats,
> atomic_long_t *mib,
> }
>
> static inline void __snmp6_fill_stats64(u64 *stats, void __percpu *mib,
> - int items, int bytes, size_t syncpoff)
> + int items, int bytes, size_t syncpoff)
> {
> - int i;
> + int i, c;
> + u64 *tmp;
> int pad = bytes - sizeof(u64) * items;
> BUG_ON(pad < 0);
>
> + tmp = kcalloc(items, sizeof(u64), GFP_KERNEL);
> +
This is a great idea, but kcalloc()/kmalloc() can fail and you'll crash
the whole kernel at this point.
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