Message-ID: <1440797172.11525.161.camel@perches.com>
Subject: Re: [PATCH RFC V2 2/2] net: Optimize snmp stat aggregation by
 walking all the percpu data at once
From: Joe Perches <joe@perches.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Miller <davem@davemloft.net>, raghavendra.kt@linux.vnet.ibm.com,
        edumazet@google.com, kuznet@ms2.inr.ac.ru, jmorris@namei.org,
        yoshfuji@linux-ipv6.org, kaber@trash.net, jiri@resnulli.us,
        hannes@stressinduktion.org, tom@herbertland.com, azhou@nicira.com,
        ebiederm@xmission.com, ipm@chirality.org.uk, nicolas.dichtel@6wind.com,
        serge.hallyn@canonical.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: Fri, 28 Aug 2015 14:26:12 -0700
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	 <1440794020.8932.45.camel@edumazet-glaptop2.roam.corp.google.com>
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On Fri, 2015-08-28 at 14:14 -0700, Eric Dumazet wrote:
> 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:
> > > > 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.

Always a possibility, but I don't think so.

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

That's why I suggested changing the snmp_fill_stats arguments.

If the naturally aligned allocated u64 array is used and then
copied as a block to the rtnetlink skb, I believe there's no
alignment issue that would require put_unaligned.

Do I still miss something?

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

I read that.

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