netdev - Re: [PATCH net-next 3/3] packet: use percpu mmap tx frame pending refcount

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Date:	Mon, 13 Jan 2014 13:57:45 +0100
From:	Daniel Borkmann <dborkman@...hat.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	Cong Wang <cwang@...pensource.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/3] packet: use percpu mmap tx frame pending
 refcount

On 01/13/2014 12:58 PM, David Laight wrote:
> From: Daniel Borkmann
> ...
>> But I think I found a different problem with this idea. It could
>> happen with net devices as well, but probably less likely as there
>> might be a better distribution of hold/puts among CPUs. However,
>> for TX_RING, if we pin the process to a particular CPU, and since
>> the destructor is invoked through ksoftirqd, we could end up with
>> a misbalance and if the process runs long enough eventually
>> overflow for one particular CPU. We could work around that, but I
>> think it's not worth the effort.
>
> The sum will be 'correct' when summed across all the cpu even if
> one of the values has wrapped - provided all the arithmetic is
> unsigned and the variables all the same type.

You are right, sorry, too much coffee this morning, I missed that.

Then, imho, this should work.
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