netdev - Re: [PATCH RFC 0/3] tun zerocopy stats

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Date:   Wed, 11 Oct 2017 17:44:10 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RFC 0/3] tun zerocopy stats

On Tue, Oct 10, 2017 at 11:15 PM, Jason Wang <jasowang@...hat.com> wrote:
>
>
> On 2017年10月11日 03:11, Willem de Bruijn wrote:
>>
>> On Tue, Oct 10, 2017 at 1:39 PM, David Miller <davem@...emloft.net> wrote:
>>>
>>> From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
>>> Date: Tue, 10 Oct 2017 11:29:33 -0400
>>>
>>>> If there is a way to expose these stats through vhost_net directly,
>>>> instead of through tun, that may be better. But I did not see a
>>>> suitable interface. Perhaps debugfs.
>>>
>>> Please don't use debugfs, thank you :-)
>>
>> Okay. I'll take a look at tracing for on-demand measurement.
>
>
> This reminds me a past series that adding tracepoints to vhost/net[1]. It
> can count zero/datacopy independently and even contains a sample program to
> show the stats.

Interesting, thanks!

For occasional evaluation, we can also use a bpf kprobe for the time being:

  bpf_program = """
  #include <uapi/linux/ptrace.h>
  #include <bcc/proto.h>

  BPF_ARRAY(count, u64, 2);

  void inc_counter(struct pt_regs *ctx) {
      bool success;
      int key;
      u64 *val;

      success = PT_REGS_PARM2(ctx);
      key = success ? 0 : 1;
      val = count.lookup(&key);
      if (val)
          lock_xadd(val, 1);
  }
  """

  b = bcc.BPF(text=bpf_program)
  b.attach_kprobe(event="vhost_zerocopy_callback", fn_name="inc_counter")

  time.sleep(5)

  print("vhost_zerocopy_callback: Y:%d N:%d" %
        (b["count"][ctypes.c_int(0)].value,
         b["count"][ctypes.c_int(1)].value))