> > 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? 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.
