netdev - Re: [PATCH bpf-next 1/5] bpf: cpumap use ptr_ring_consume

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Message-ID: <20190411132339.5427313b@carbon>
Date:   Thu, 11 Apr 2019 13:23:39 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        bpf <bpf@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        brouer@...hat.com
Subject: Re: [PATCH bpf-next 1/5] bpf: cpumap use ptr_ring_consume_batched

On Wed, 10 Apr 2019 16:24:37 -0700
Song Liu <liu.song.a23@...il.com> wrote:

> >                 /* Feedback loop via tracepoint */
> > -               trace_xdp_cpumap_kthread(rcpu->map_id, processed, drops, sched);
> > +               trace_xdp_cpumap_kthread(rcpu->map_id, n, drops, sched);  
> 
> btw: can we do the tracepoint after local_bh_enable()?

I would rather not, as my experience is that this result in strange
inaccurate readings, because (as comment below says) this is a
CPU-process-reschedule point.  The test tool reads these values and
calculate PPS.

> >
> >                 local_bh_enable(); /* resched point, may call do_softirq() */
> >         }

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer