netdev - Re: [RFC net-next 1/2] net: net-porcfs: Reduce rcu lock critical section

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Message-ID: <75137dbf-4608-127e-1601-10a3c13e3a32@gmail.com>
Date:   Tue, 10 Apr 2018 13:35:22 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>, saeedm@...lanox.com
Cc:     netdev@...r.kernel.org
Subject: Re: [RFC net-next 1/2] net: net-porcfs: Reduce rcu lock critical
 section



On 04/10/2018 10:16 AM, David Miller wrote:
> 
> The tradeoff here is that now you are doing two unnecessary atomic
> operations per stats dump.
> 
> That is what the RCU lock allows us to avoid.
> 

dev_hold() and dev_put() are actually per cpu increment and decrements,
pretty cheap these days.

Problem here is that any preemption of the process holding device reference
might trigger warnings in device unregister.