netdev - Re: [PATCH net-next-2.6] loopback: Implement 64bit stats on 32bit arches

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Date:	Tue, 15 Jun 2010 16:49:23 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org,
	bhutchings@...arflare.com
Subject: Re: [PATCH net-next-2.6] loopback: Implement 64bit stats on 32bit
 arches

On Mon, Jun 14, 2010 at 11:14:12PM -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Mon, 14 Jun 2010 17:59:22 +0200
> 
> > Uses a seqcount_t to synchronize stat producer and consumer, for packets
> > and bytes counter, now u64 types.
> > 
> > (dropped counter being rarely used, stay a native "unsigned long" type)
> > 
> > No noticeable performance impact on x86, as it only adds two increments
> > per frame. It might be more expensive on arches where smp_wmb() is not
> > free.
> > 
> > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> 
> Applied, but I suspect we might end up eventually needing to
> abstract this kind of technique in a common place so other
> spots can use it.

Check i_size stuff in include/linux/fs.h if you consider doing this.
And keep preempt in mind too. I assume you can't be preempted at this
point, but if you're prone to change the locking, it might be worth
the (small) cost of doing explicit preempt_disable() (and maybe to
help the sanity of the -rt guys too).

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