linux-kernel - Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once

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Message-Id: <20150828.112413.424099339331017970.davem@davemloft.net>
Date:	Fri, 28 Aug 2015 11:24:13 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	raghavendra.kt@...ux.vnet.ibm.com
Cc:	edumazet@...gle.com, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, jiri@...nulli.us,
	hannes@...essinduktion.org, tom@...bertland.com, azhou@...ira.com,
	ebiederm@...ssion.com, ipm@...rality.org.uk,
	nicolas.dichtel@...nd.com, serge.hallyn@...onical.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	anton@....ibm.com, nacc@...ux.vnet.ibm.com,
	srikar@...ux.vnet.ibm.com
Subject: Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by
 walking all the percpu data at once

From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Date: Fri, 28 Aug 2015 12:09:52 +0530

> On 08/28/2015 12:08 AM, David Miller wrote:
>> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>> Date: Wed, 26 Aug 2015 23:07:33 +0530
>>
>>> @@ -4641,10 +4647,12 @@ static inline void __snmp6_fill_stats64(u64
>>> *stats, void __percpu *mib,
>>>   static void snmp6_fill_stats(u64 *stats, struct inet6_dev *idev, int
>>>   attrtype,
>>>   			     int bytes)
>>>   {
>>> +	u64 buff[IPSTATS_MIB_MAX] = {0,};
>>> +
 ...
> hope you wanted to know the overhead than to change the current
> patch. please let me know..

I want you to change that variable initializer to an explicit memset().

The compiler is emitting a memset() or similar _anyways_.

Not because it will have any impact at all upon performance, but because
of how it looks to people trying to read and understand the code.
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