Date:	Sat, 01 Mar 2008 12:22:30 +0100
From:	Oliver Hartkopp <oliver@...tkopp.net>
To:	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: Patch: [NET]: Remove CONFIG_PROC_FS depency for pcounter inuse

Eric Dumazet wrote:
> Oliver Hartkopp a écrit :
>> Hi all,
>>
>> attached you'll find a patch that fixes the depency that has been 
>> introduced in commit 65f7651788e18fadb2fbb7276af935d7871e1803 ([NET]: 
>> prot_inuse cleanups and optimizations).
>>
>> As the inuse counters are only used by internet protocols right now, 
>> using CONFIG_INET would have been more obvious to recognize this 
>> illegal optimization here. Going a bit deeper into this problem we 
>> can see, that the pcounters are ONLY used for the internet protocols 
>> BUT initialized for ALL protocols in proto_[un|]register() in 
>> net/core/sock.c.
>>
>> This forces all network protocols to initialize the pcounters and 
>> therefore request dynamic percpu memory even when it is not used at all.
>>
>> I would suggest to
>>
>> 1. move the ..._inuse_[init|free]() stuff from sock.c to 
>> af_inet[|6].c and his friends
>>
>> OR
>>
>> 2. add new parameters to proto_[un|]register() like 'alloc_inuse' and 
>> 'free_inuse'
>>
>> My favourite sollution would be the second one but before creating a 
>> patch for one of these suggestions, i wanted to ask for your opinion 
>> or if there is any 'even nicer' idea from your side.
>
> Hello Oliver
>
> I am just coming back from hollidays.

Lucky guy ;-)

>
> Last thing I did before leaving was to post a patch to correct 
> performance hit of percpu_counters in mainline. ([PATCH] 
> alloc_percpu() fails to allocate percpu data 
> http://lkml.org/lkml/2008/2/21/254 )
>
> Before accepting Andrew Morton claims about percpu_counters being 
> superior to pcounter, I benched them and found they were not.
>
> As soon as percpu_counters are not grossly inefficient, the only move 
> will be to just zap pcounter, as most people dont like it.
>
> Only one patch will be necessary, please dont try to hide pcounter by 
> small patches :)

Hm - i followed the discussion in it's major parts but my RFC hit's the 
question whether the integration of the what-ever-per-cpu-counter 
initialisation in proto_register() and proto_unregister() is the right 
way as only the internet protocols (v4/v6) are using inuse counters 
these days.

It's not about the counter implementation but the integration/usage in 
the networking subsystem.

Or does your mentioned patch mean, that the added functions in 
proto_[un|]register() will also be reverted?

Regards,
Oliver

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