netdev - Re: [PATCH 3/4] flowcache: make struct flow_cache_percpu::hash_rnd

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Message-Id: <20170321.190948.1404708055619408272.davem@davemloft.net>
Date:   Tue, 21 Mar 2017 19:09:48 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     adobriyan@...il.com
Cc:     steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
        netdev@...r.kernel.org
Subject: Re: [PATCH 3/4] flowcache: make struct
 flow_cache_percpu::hash_rnd_recalc bool

From: Alexey Dobriyan <adobriyan@...il.com>
Date: Mon, 20 Mar 2017 01:27:43 +0300

> ->hash_rnd_recalc is only used in boolean context.
> 
> Space savings on x86_64 come from the fact that "MOV rm8, imm8" is
> shorter than "MOV rm32, imm32" by at least 3 bytes.
> 
> 	add/remove: 0/0 grow/shrink: 0/3 up/down: 0/-10 (-10)
> 	function                                     old     new   delta
> 	flow_cache_new_hashrnd                       166     163      -3
> 	flow_cache_cpu_up_prep                       171     168      -3
> 	flow_cache_lookup                           1148    1144      -4
> 	Total: Before=170822872, After=170822862, chg -0.00%
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>

I agree with Eric Dumazet that we might have atomicity issues in the
future because of this change.

Why don't you drop this and resubmit just the other 3 patches which
seem to be much less controversial?

Thanks.