Re: [PATCH] ppp: add 64 bit stats

[Eric Dumazet <eric.dumazet@gmail.com>]

On Sun, 2012-07-22 at 16:19 -0400, Kevin Groeneveld wrote:
> Add 64 bit stats to ppp driver.  The 64 bit stats include tx_bytes,
> rx_bytes, tx_packets and rx_packets.  Other stats are still 32 bit.
> The 64 bit stats can be retrieved via the ndo_get_stats operation.  The
> SIOCGPPPSTATS ioctl is still 32 bit stats only.
> 
> Signed-off-by: Kevin Groeneveld <kgroeneveld@gmail.com>
> ---
>  drivers/net/ppp/ppp_generic.c |  110 +++++++++++++++++++++++++++++++++++------
>  1 file changed, 95 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
> index 5c05572..210238c 100644
> --- a/drivers/net/ppp/ppp_generic.c
> +++ b/drivers/net/ppp/ppp_generic.c
> @@ -94,6 +94,19 @@ struct ppp_file {
>  #define PF_TO_CHANNEL(pf)	PF_TO_X(pf, struct channel)
>  
>  /*
> + * Data structure to hold primary network stats for which
> + * we want to use 64 bit storage.  Other network stats
> + * are stored in dev->stats of the ppp strucute.
> + */
> +struct ppp_link_stats {
> +	struct u64_stats_sync syncp;
> +	u64 tx_bytes;
> +	u64 tx_packets;
> +	u64 rx_bytes;
> +	u64 rx_packets;
> +};

Hmm. This patches adds races, but also adds a good amount of memory on
these servers with thousand of ppp devices, and 64 cpus.

I really doubt ppp is performance sensitive, it so doesnt need percpu
counter.

If you really want 64bits stats on ppp, use proper synchronization
around u64 counters (but shared ones)