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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Date:	Fri, 28 Aug 2015 14:14:47 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>,
	raghavendra.kt@...ux.vnet.ibm.com, 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 Fri, 2015-08-28 at 14:09 -0700, Joe Perches wrote:
> On Fri, 2015-08-28 at 13:55 -0700, Eric Dumazet wrote:
> > On Fri, 2015-08-28 at 13:53 -0700, Joe Perches wrote:
> > > On Fri, 2015-08-28 at 13:33 -0700, Eric Dumazet wrote:
> > > > We do not bother for small struct.
> > > > 
> > > > Here, the array is big enough that David prefers having an explicit
> > > > memset() so that it clearly shows that author of this code was aware of
> > > > this.
> > > 
> > > It's 288 bytes on stack, maybe a kzalloc would be clearer too.
> > 
> > Could you read patch history and check why this has been rejected ?
> 
> I don't see a rejection, just that the initial
> submission didn't check the allocation or add
> an allocation buffer via kcalloc/kzalloc to the
> inet6_fill_ifla6_attrs caller and change the
> snmp6_fill_stats arguments.
> 
> It could also eliminate the put_unaligned calls.

Not really. You do not properly read this code.

put_unaligned is happening on a space allocated from rtnetlink skb, not
the temp space needed to perform the per cpu folding.

> 
> https://lkml.org/lkml/2015/8/25/114
> 
> Was there some other thread?

Same thread

https://lkml.org/lkml/2015/8/25/476



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