netdev - Re: 64-bit net_device

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Message-ID: <20100604015956.GA10971@host-a-55.ustcsz.edu.cn>
Date:	Fri, 4 Jun 2010 09:59:59 +0800
From:	Junchang Wang <junchangwang@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	David Miller <davem@...emloft.net>, romieu@...zoreil.com,
	netdev@...r.kernel.org
Subject: Re: 64-bit net_device_stats

Hi Ben,

On Wed, Jun 02, 2010 at 10:34:29PM +0100, Ben Hutchings wrote:
>Changing the counter types to u64 for 32-bit architectures would remove
>atomicity and expose half-updated counters to userland.  Changing the
>driver interface significantly so that atomicity is not needed would
>require changes to hundreds of drivers.
>
>Assuming the above is all correct, I think we can only solve this with a
>gradual change (as for net_device_ops).  The following might work:
>
I realized the network team doesn't care about 64-bit counters (especially rx_*) on 32-bit systems. A similar disscussion can be found here:
http://www.gossamer-threads.com/lists/linux/kernel/282631?search_string=64%20stats;#282631

And Eric just gave a explanation why they stand by that point. Updating rx_* counters in core network will dirty a cache line.

--Junchang
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