netdev - Re: [Intel-wired-lan] [PATCH bpf-next 2/6] samples/bpf: increment Tx stats at sending

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Message-ID: <CAJ8uoz1f=-2Dysg-iwo=Grn0eS5nJB0hNE8HuPeHYPgeE4Bfmg@mail.gmail.com>
Date:   Tue, 10 Nov 2020 08:12:54 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Maciej Fijalkowski <maciejromanfijalkowski@...il.com>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH bpf-next 2/6] samples/bpf: increment Tx
 stats at sending

On Mon, Nov 9, 2020 at 9:47 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> Magnus Karlsson wrote:
> > From: Magnus Karlsson <magnus.karlsson@...el.com>
> >
> > Increment the statistics over how many Tx packets have been sent at
> > the time of sending instead of at the time of completion. This as a
> > completion event means that the buffer has been sent AND returned to
> > user space. The packet always gets sent shortly after sendto() is
> > called. The kernel might, for performance reasons, decide to not
> > return every single buffer to user space immediately after sending,
> > for example, only after a batch of packets have been
> > transmitted. Incrementing the number of packets sent at completion,
> > will in that case be confusing as if you send a single packet, the
> > counter might show zero for a while even though the packet has been
> > transmitted.
> >
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> > ---
>
> LGTM. Just one question then if we wanted to know the old value, packet
> completion counter it looks like (tx_npkts - outstanding_tx) would give
> that value?

That is correct.

> Acked-by: John Fastabend <john.fastabend@...il.com>