Song, Yoong Siang wrote: > On Monday, December 4, 2023 10:58 PM, Willem de Bruijn wrote: > >Song, Yoong Siang wrote: > >> On Friday, December 1, 2023 11:02 PM, Jesper Dangaard Brouer wrote: > >> >On 12/1/23 07:24, Song Yoong Siang wrote: > >> >> This patch enables txtime support to XDP zero copy via XDP Tx > >> >> metadata framework. > >> >> > >> >> Signed-off-by: Song Yoong Siang<yoong.siang.song@xxxxxxxxx> > >> >> --- > >> >> drivers/net/ethernet/stmicro/stmmac/stmmac.h | 2 ++ > >> >> drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 +++++++++++++ > >> >> 2 files changed, 15 insertions(+) > >> > > >> >I think we need to see other drivers using this new feature to evaluate > >> >if API is sane. > >> > > >> >I suggest implementing this for igc driver (chip i225) and also for igb > >> >(i210 chip) that both support this kind of LaunchTime feature in HW. > >> > > >> >The API and stmmac driver takes a u64 as time. > >> >I'm wondering how this applies to i210 that[1] have 25-bit for > >> >LaunchTime (with 32 nanosec granularity) limiting LaunchTime max 0.5 > >> >second into the future. > >> >And i225 that [1] have 30-bit max 1 second into the future. > >> > > >> > > >> >[1] > >> >https://github.com/xdp-project/xdp- > >> >project/blob/master/areas/tsn/code01_follow_qdisc_TSN_offload.org > >> > >> I am using u64 for launch time because existing EDT framework is using it. > >> Refer to struct sk_buff below. Both u64 and ktime_t can be used as launch time. > >> I choose u64 because ktime_t often requires additional type conversion and > >> we didn't expect negative value of time. > >> > >> include/linux/skbuff.h-744- * @tstamp: Time we arrived/left > >> include/linux/skbuff.h:745- * @skb_mstamp_ns: (aka @tstamp) earliest departure > >time; start point > >> include/linux/skbuff.h-746- * for retransmit timer > >> -- > >> include/linux/skbuff.h-880- union { > >> include/linux/skbuff.h-881- ktime_t tstamp; > >> include/linux/skbuff.h:882- u64 skb_mstamp_ns; /* earliest departure > >time */ > >> include/linux/skbuff.h-883- }; > >> > >> tstamp/skb_mstamp_ns are used by various drivers for launch time support > >> on normal packet, so I think u64 should be "friendly" to all the drivers. For an > >> example, igc driver will take launch time from tstamp and recalculate it > >> accordingly (i225 expect user to program "delta time" instead of "time" into > >> HW register). > >> > >> drivers/net/ethernet/intel/igc/igc_main.c-1602- txtime = skb->tstamp; > >> drivers/net/ethernet/intel/igc/igc_main.c-1603- skb->tstamp = ktime_set(0, 0); > >> drivers/net/ethernet/intel/igc/igc_main.c:1604- launch_time = > >igc_tx_launchtime(tx_ring, txtime, &first_flag, &insert_empty); > >> > >> Do you think this is enough to say the API is sane? > > > >u64 nsec sounds sane to be. It must be made explicit with clock source > >it is against. > > > > The u64 launch time should base on NIC PTP hardware clock (PHC). > I will add documentation saying which clock source it is against It's not that obvious to me that that is the right and only choice. See below. > >Some applications could want to do the conversion from a clock source > >to raw NIC cycle counter in userspace or BPF and program the raw > >value. So it may be worthwhile to add an clock source argument -- even > >if initially only CLOCK_MONOTONIC is supported. > > Sorry, not so understand your suggestion on adding clock source argument. > Are you suggesting to add clock source for the selftest xdp_hw_metadata apps? > IMHO, no need to add clock source as the clock source for launch time > should always base on NIC PHC. This is not how FQ and ETF qdiscs pass timestamps to drivers today. Those are in CLOCK_MONOTONIC or CLOCK_TAI. The driver is expected to convert from that to its descriptor format, both to the reduced bit width and the NIC PHC. See also for instance how sch_etf has an explicit q->clock_id match, and SO_TXTIME added an sk_clock_id for the same purpose: to agree on which clock source is being used.
