> From: Stefan Lässer [mailto:stefan.laes...@omicronenergy.com] > Sent: Friday, 6 September 2024 08.23 > > > > From: Stephen Hemminger [mailto:step...@networkplumber.org] > > > Sent: Tuesday, 3 September 2024 18.22 > > > > > > On Tue, 3 Sep 2024 13:43:06 +0200 > > > Stefan Laesser <stefan.laes...@omicronenergy.com> wrote: > > > > > > > Add the packet timestamp from TPACKET_V2 to the mbuf dynamic rx > > > > timestamp register if offload RTE_ETH_RX_OFFLOAD_TIMESTAMP is > > > > enabled. > > > > > > > > TPACKET_V2 provides the timestamp with nanosecond resolution. > > > > > > > > Signed-off-by: Stefan Laesser <stefan.laes...@omicronenergy.com> > > > > --- > > > > .mailmap | 1 + > > > > doc/guides/nics/af_packet.rst | 8 ++++-- > > > > drivers/net/af_packet/rte_eth_af_packet.c | 34 > > > > +++++++++++++++++++++- > > > - > > > > 3 files changed, 38 insertions(+), 5 deletions(-) > > > > > > Adding timestamp is good, but it would be better if the timestamp > > > field was generic. The pcap PMD also has a timestamp, and pdump API > > > could/should use timestamp as well. > > > > As far as I can see, this patch does use the existing cross-driver/generic > > timestamp dynamic field, like the pcap driver. > > Yes, I use the generic timestamp dynamic field as used in all the other PMDs I > have looked at. > > > > > > > > > What makes sense is for there to be a standard dynamic field for > > > nanosecond resolution timestamp, and add a make sure that all drivers > > > use the same base 1/1/1970 same as Linux/Unix. > > > > Yes, standardizing on nanosecond resolution and a common base might have > > been a better choice than using driver-specific units for the generic > > timestamp dynamic field. > > If the driver can use the NIC's native clock system, the driver doesn't need > to > > convert to nanoseconds, which has a performance cost. > > However, I suppose any application using timestamps needs to do this > > conversion in the application instead, so the total performance is the same > as > > if the drivers did it. I.e. from a performance perspective, the drivers > might as > > well do the conversion, and from a usability perspective, it would be easier > > with a standard unit and base. > > > > We should define a roadmap towards dynamic mbuf field timestamps using > > fixed unit and base (instead of driver-specific) and migrate towards it. > > > > Perhaps start by adding an ethdev capability flag, > > RTE_ETH_RX_OFFLOAD_TIMESTAMP_NS used together with > > RTE_ETH_RX_OFFLOAD_TIMESTAMP to indicate that the timestamp unit and > > base follows a common standard, i.e. nanoseconds since UNIX epoch. > > > > There may be other considerations, though: The NIC's clock may drift > > compared to the CPU's clock, and compared to the clock of other NICs in the > > same system. So the "base" and "nanoseconds" will still be using the NIC's > > clock as reference, and it might be way out of sync with the CPU's clock. > > > > > Also, having > > > standard helpers in ethdev for the conversion from TSC to NS would > > > help. > > > > Helpers to convert from CPU TSC to nanoseconds have broader scope than > > ethdev and belong in the EAL, perhaps in > > /lib/eal/include/generic/rte_cycles.h? > > Should I extend my patch to include the new RTE_ETH_RX_OFFLOAD_TIMESTAMP_NS > capability?
That would be nice, but not a requirement. :-) Please do it as a series of patches, maybe three: 1. This patch. 2. A patch to generally introduce TIMESTAMP_NS RX offload and capability flags. 3. A patch to implement TIMESTAMP_NS in af_packet. The new TIMESTAMP_NS feature might trigger some discussions, and you don't want this patch caught up too much in that discussion. > What happens if the user only enables RTE_ETH_RX_OFFLOAD_TIMESTAMP in the > AF_PACKET PMD? > I would suggest that in this case the timestamp will have microsecond accuracy > and only if RTE_ETH_RX_OFFLOAD_TIMESTAMP_NS is also enabled, then the > timestamp will have nanosecond accuracy. There's no need for different timestamp accuracy if TIMESTAMP_NS is not enabled. RTE_ETH_RX_OFFLOAD_TIMESTAMP means that a timestamp is present, with driver dependent clock and base. The driver is allowed to use nanoseconds as clock and UNIX origo as base, regardless.
