netdev - Re: [PATCH net-next v2 8/9] nfp: add a stats handler for flower offloads

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Date:   Thu, 29 Jun 2017 17:27:52 +0200
From:   Simon Horman <simon.horman@...ronome.com>
To:     Or Gerlitz <gerlitz.or@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        oss-drivers@...ronome.com,
        Pieter Jansen van Vuuren 
        <pieter.jansenvanvuuren@...ronome.com>
Subject: Re: [PATCH net-next v2 8/9] nfp: add a stats handler for flower
 offloads

On Thu, Jun 29, 2017 at 06:16:41PM +0300, Or Gerlitz wrote:
> On Wed, Jun 28, 2017 at 11:30 PM, Simon Horman
> <simon.horman@...ronome.com> wrote:
> > From: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@...ronome.com>
> >
> > Previously there was no way of updating flow rule stats after they
> > have been offloaded to hardware. This is solved by keeping track of
> > stats received from hardware and providing this to the TC handler
> > on request.
> 
> > +static void
> > +nfp_flower_update_stats(struct nfp_app *app, struct nfp_fl_stats_frame *stats)
> > +{
> > +       struct nfp_fl_payload *nfp_flow;
> > +       unsigned long flower_cookie;
> > +
> > +       flower_cookie = be64_to_cpu(stats->stats_cookie);
> > +
> > +       rcu_read_lock();
> > +       nfp_flow = nfp_flower_find_in_fl_table(app, flower_cookie);
> > +       if (!nfp_flow)
> > +               goto exit_rcu_unlock;
> > +
> > +       if (nfp_flow->meta.host_ctx_id != stats->stats_con_id)
> > +               goto exit_rcu_unlock;
> > +
> > +       spin_lock(&nfp_flow->lock);
> > +       nfp_flow->stats.pkts += be32_to_cpu(stats->pkt_count);
> > +       nfp_flow->stats.bytes += be64_to_cpu(stats->byte_count);
> 
> you're using += with the values you get form the fw, are they incremental?

Yes, they are incremental.

> 
> > +       nfp_flow->stats.used = jiffies;
> 
> if nothing was changed since your last reading, it's wrong to say that
> used == NOW

This function is called on receipt of a message from the firmware.
And the firmware will only send a message if there is a change in
the counters.

> 
> > +       spin_unlock(&nfp_flow->lock);
> 
> if indeed you need to keep a clone of earlier calls to correctly
> compute the (last)used value,
> maybe you can get rid of the locking?