netdev - Re: [PATCH] ppp: add 64 bit stats

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Message-ID: <CABF+-6Wpn8yEvru1FDsaFbXYZ7tyeQqqbEU2VY8hLKvmXXFBXA@mail.gmail.com>
Date:	Tue, 24 Jul 2012 22:27:03 -0400
From:	Kevin Groeneveld <kgroeneveld@...il.com>
To:	netdev@...r.kernel.org
Subject: Re: [PATCH] ppp: add 64 bit stats

On Tue, Jul 24, 2012 at 2:22 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2012-07-23 at 21:53 -0400, Kevin Groeneveld wrote:
>> On Mon, Jul 23, 2012 at 11:59 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> >> Would proper synchronization in this case just be wrapping the updates
>> >> in a spin_lock/spin_unlock?
>> >
>> > Would be fine (if the proper BH safe variant is used), or you could also
>> > use atomic64_t.
>>
>> Which would you recommend, spin locks or atomic64_t?
>>
>> atomic64_t seems like it would be simpler.
>
> Simpler but a bit more expensive when two counters are changed at the
> same time.
>
> (two atomic ops instead of a single one for the spinlock)

After looking at the existing ppp code more I wonder if I would even
need to add my own spinlocks.  It seems the only spots I am updating
the 64 bit stats are already protected by either ppp->wlock or
ppp->rlock spinlocks.  If I used two separate u64_stats_sync
structures, one for tx stats and one for rx stats, wouldn't the
existing spinlocks be enough?
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