Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755443AbbHYO2f (ORCPT <rfc822;w@1wt.eu>);
	Tue, 25 Aug 2015 10:28:35 -0400
Received: from mail-pa0-f54.google.com ([209.85.220.54]:33566 "EHLO
	mail-pa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752059AbbHYO2d (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 25 Aug 2015 10:28:33 -0400
Message-ID: <1440512908.8932.11.camel@edumazet-glaptop2.roam.corp.google.com>
Subject: Re: [PATCH RFC 2/2] net: Optimize snmp stat aggregation by walking
 all the percpu data at once
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: davem@davemloft.net, kuznet@ms2.inr.ac.ru, jmorris@namei.org,
        yoshfuji@linux-ipv6.org, kaber@trash.net, jiri@resnulli.us,
        edumazet@google.com, hannes@stressinduktion.org, tom@herbertland.com,
        azhou@nicira.com, ebiederm@xmission.com, ipm@chirality.org.uk,
        nicolas.dichtel@6wind.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, anton@au1.ibm.com,
        nacc@linux.vnet.ibm.com, srikar@linux.vnet.ibm.com
Date: Tue, 25 Aug 2015 07:28:28 -0700
In-Reply-To: <1440489266-31127-3-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
References: <y>
	 <1440489266-31127-1-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
	 <1440489266-31127-3-git-send-email-raghavendra.kt@linux.vnet.ibm.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.10.4-0ubuntu2 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 2471
Lines: 66

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.kt@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.



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/