netdev - Re: [PATCH v1 net-next] tuntap: convert to 64-bit interface statistics

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Message-ID: <1426813457.25985.24.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 19 Mar 2015 18:04:17 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jonathan Toppins <jtoppins@...ulusnetworks.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Curt Brune <curt@...ulusnetworks.com>
Subject: Re: [PATCH v1 net-next] tuntap: convert to 64-bit interface
 statistics

On Thu, 2015-03-19 at 19:52 -0400, Jonathan Toppins wrote:
> On 3/19/15 6:56 PM, Eric Dumazet wrote:
> > On Thu, 2015-03-19 at 17:56 -0400, Jonathan Toppins wrote:
> >
> >
> >> Or are you suggesting per-cpu counters would be preferred which would
> >> possibly eliminate the need for this lock?
> >
> > Might be overkill for a device that is probably used by one cpu,
> > considering you defined a full  struct rtnl_link_stats64, instead of the
> > fields that are really handled.
> >
> 
> Ok. So summarizing for v2, so far; eliminating the back-to-back lock -> 
> release -> lock -> release is preferred (I agree with this).
> 
> It still seems like you are not a huge fan of the additional lock, 
> should I hold off on sending v2 for a day, so we can ponder alternatives?

It seems you need a lock only in RX, for 2 vars only.
(rx_packets & rx_bytes)

error counters are generally OK with unsigned long, nobody will complain
of possible concurrent non atomic updates.

So maybe percpu var for these 16 bytes would be OK.



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