On Mon, 15 Dec 2003 18:19:27 -0500 (EST) Donald Becker <becker@xxxxxxxxx> wrote:
| On Mon, 15 Dec 2003, Randy.Dunlap wrote:
| > On Mon, 15 Dec 2003 14:17:29 -0800 "David S. Miller" <davem@xxxxxxxxxx>
| > | On Mon, 15 Dec 2003 12:03:58 -0800
| > | Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote:
| > |
| > | > Is there an agreed upon standard for exactly what ethernet drivers
| > | > should be counting for rx-bytes and tx-bytes? For example, should the
| > | > counters include the 4-byte FCS?
| > | > Should they include the ethernet header?
| Yes, but not the preamble.
| [[ Ethernet packets have an 8 byte preamble before the station
| addresses. It doesn't make sense to count this, as
| all modern NICs strip it off, and
| a few leading bits may be dropped at each hop
| > | It should be that all drivers use what skb->len ends up with at
| > | rx/tx time.
| Not quite. The skb->len value omits the 4 byte FCS/CRC.
| > | However, it is often faster to just let the hardware keep track
| > | of these statistics (tg3 is one example of a chip that can do
| > | this). And sometimes these mechanisms take the FCS or whatever
| > | into account and this as you note makes the numbers different.
| The driver should correct, although this is non-critical.
| Using hardware counters where available used to make sense, but today
| it's better to have the software driver maintain the statistics. The
| only thing the hardware counters are needed for is
| otherwise-unobservable errors, such as missed packets and CRC errors.
| > RFC 1573:
| > RFC 2233:
| > RFC 1213:
| > all agree that on an "interface" the number of octets received (InOctets)
| > is:
| > The total number of octets received on the interface, including
| > framing characters.
| This is imprecise. "Framing" might be misread to include the preamble,
| which should be omitted from the count.
| The original Linux errors counters were influenced by what the dp8390
| chip reported. Later, the definitions in appendix B of the dc21040
| manual served as a more general guideline (although the software
| counters were never a one-for-one copy of any specific hardware
I agree with Don's comments, based on my experiences in former lives.
I don't know about the DC21040, but I worked at/on both National and
Intel LAN drivers.
MOTD: Always include version info.