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: <55E164C6.3000702@linux.vnet.ibm.com>
Date:	Sat, 29 Aug 2015 13:22:38 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, 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

On 08/29/2015 08:56 AM, Eric Dumazet wrote:
> On Sat, 2015-08-29 at 08:27 +0530, Raghavendra K T wrote:
>>
>>   	/* Use put_unaligned() because stats may not be aligned for u64. */
>>   	put_unaligned(items, &stats[0]);
>
>
>>   	for (i = 1; i < items; i++)
>> -		put_unaligned(snmp_fold_field64(mib, i, syncpoff), &stats[i]);
>> +		put_unaligned(buff[i], &stats[i]);
>>
>
> I believe Joe suggested following code instead :
>
> buff[0] = items;
> memcpy(stats, buff, items * sizeof(u64));

Thanks. Sure, will use this.

(I missed that. I thought that it was applicable only when we have
aligned data,and for power, put_aunaligned was not a nop unlike intel).

>
> Also please move buff[] array into __snmp6_fill_stats64() to make it
> clear it is used in a 'leaf' function.

Correct.

>
> (even if calling memcpy()/memset() makes it not a leaf function)
>

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