linux-kernel - Re: [PATCH RFC 0/2] Optimize the snmp stat aggregation for large cpus

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Message-ID: <55DD9401.9090809@linux.vnet.ibm.com>
Date:	Wed, 26 Aug 2015 15:55:05 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
CC:	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, jiri@...nulli.us, edumazet@...gle.com,
	hannes@...essinduktion.org, tom@...bertland.com, azhou@...ira.com,
	ebiederm@...ssion.com, ipm@...rality.org.uk,
	nicolas.dichtel@...nd.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 0/2] Optimize the snmp stat aggregation for large
 cpus

On 08/26/2015 04:37 AM, David Miller wrote:
> From: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> Date: Tue, 25 Aug 2015 13:24:24 +0530
>
>> Please let me know if you have suggestions/comments.
>
> Like Eric Dumazet said the idea is good but needs some adjustments.
>
> You might want to see whether a per-cpu work buffer works for this.

sure, Let me know if I understood correctly,

we allocate the temp buffer,
we will have a  "add_this_cpu_data" function and do

for_each_online_cpu(cpu)
                 smp_call_function_single(cpu, add_this_cpu_data, buffer, 1)

if not could you please point to an example you had in mind.

>
> It's extremely unfortunately that we can't depend upon the destination
> buffer being properly aligned, because we wouldn't need a temporary
> scratch area if it were aligned properly.

True, But I think for 64 bit cpus when (pad == 0) we can go ahead and
use stats array directly and get rid of put_unaligned(). is it correct?

(my internal initial patch had this version but thought it is ugly to
have ifdef BITS_PER_LONG==64)




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