On Thu, Sep 21, 2023 at 5:09 AM Stephen Hemminger <[email protected]> wrote: > > On Wed, 20 Sep 2023 22:55:21 +0300 > Isaac Boukris <[email protected]> wrote: > > > I found a way to get a better resolution; at init we set > > 'pcapng_time.tsc_hz=rte_get_tsc_hz()/NSEC_PER_SEC' this way we keep > > the number of cycles in a nano-second, then at run time we just need > > to divide delta by this number (with no need to multiply by > > NSEC_PER_SEC). > > > > The problem is I guess, that on slow systems we'll end up with > > tsc_hz=0? Perhaps we'd need to drop to ms resolution in such a case. > > > > With the attach patch I get: > > > > 2023-09-20 10:22:13.579219 IP Rocky8 > A: ICMP echo request, id 13, > > seq 63, length 64 > > 2023-09-20 10:22:13.580582 IP A > Rocky8: ICMP echo reply, id 13, seq > > 63, length 64 3 > > 2023-09-20 10:22:14.745176 IP Rocky8 > A: ICMP echo request, id 13, > > seq 64, length 64 > > 2023-09-20 10:22:14.746206 IP ... > > > > On Wed, Sep 20, 2023 at 9:53 PM Isaac Boukris <[email protected]> wrote: > > > > > > I figured the first packet bug, fixed with: > > > - if (!pcapng_time.tsc_hz) > > > + if (!pcapng_time.tsc_hz) { > > > pcapng_init(); > > > + return pcapng_time.ns; > > > + } > > > > > > However I noticed a caveat with my proposed fix as it seem we only get > > > a time resolution of one sec: > > > > > > 2023-09-20 09:40:20.727638 IP Rocky8 > A: ICMP echo request, id 11, > > > seq 81, length 64 > > > 2023-09-20 09:40:20.727638 IP A > Rocky8: ICMP echo reply, id 11, seq > > > 81, length 64 > > > 2023-09-20 09:40:21.727638 IP ... > > > > > > On Wed, Sep 20, 2023 at 8:59 PM Isaac Boukris <[email protected]> wrote: > > > > > > > > On Tue, Sep 19, 2023 at 9:00 PM Stephen Hemminger > > > > <[email protected]> wrote: > > > > > > > > > > On Tue, 19 Sep 2023 19:35:55 +0300 > > > > > Isaac Boukris <[email protected]> wrote: > > > > > > > > > > > Looking with git log, i found the original line was: > > > > > > return pcapng_time.ns + (delta * NSEC_PER_SEC) / rte_get_tsc_hz(); > > > > > > > > > > > > Testing that does show a wrapping issue, e.g. (it stays around > > > > > > 08:05). > > > > > > > > > > > > 2023-09-19 08:05:24.372037 IP _gateway.domain > Rocky8.38358: 31975 > > > > > > NXDomain 0/0/0 (46) 10 > > > > > > 2023-09-19 08:05:21.577497 ARP, Request who-has _gateway tell > > > > > > Rocky8, > > > > > > length 46 > > > > > > 2023-09-19 08:05:21.577599 ARP, Reply _gateway is-at > > > > > > 00:50:56:f8:92:76 > > > > > > (oui Unknown), length 46 13 > > > > > > 2023-09-19 08:05:22.833897 IP 192.168.202.1.50886 > > > > > > > 239.255.255.250.ssdp: UDP, length 174 > > > > > > > > > > > > However with my change it looks fine and always increments. I > > > > > > dropped > > > > > > all the parenthesis: > > > > > > return pcapng_time.ns + delta / pcapng_time.tsc_hz * NSEC_PER_SEC; > > > > > > > > > > The issue is that timestamping is in the fast path and that 64 bit > > > > > divide is slow. > > > > > Looking at other alternatives. > > > > > > > > Then perhaps we can keep the division optimization and just get rid of > > > > the overflow check, relying on the change to multiply by NSEC_PER_SEC > > > > after the division. > > > > > > > > With the below change only the first packet is from 2257 while all > > > > subsequent packets are fine. But if I keep the overflow check and only > > > > change to multiply after the division, then all packets are shown from > > > > 2257. > > > > > > > > [admin@Rocky8 dpdk]$ git diff lib/pcapng/rte_pcapng.c > > > > diff --git a/lib/pcapng/rte_pcapng.c b/lib/pcapng/rte_pcapng.c > > > > index 80d08e1..fa545cd 100644 > > > > --- a/lib/pcapng/rte_pcapng.c > > > > +++ b/lib/pcapng/rte_pcapng.c > > > > @@ -79,7 +79,7 @@ static uint64_t pcapng_tsc_to_ns(uint64_t cycles) > > > > * Currently all TSCs operate below 5GHz. > > > > */ > > > > delta = cycles - pcapng_time.cycles; > > > > - if (unlikely(delta >= pcapng_time.tsc_hz)) { > > > > + if (0 && unlikely(delta >= pcapng_time.tsc_hz)) { > > > > if (likely(delta < pcapng_time.tsc_hz * 2)) { > > > > delta -= pcapng_time.tsc_hz; > > > > pcapng_time.cycles += pcapng_time.tsc_hz; > > > > @@ -92,8 +92,9 @@ static uint64_t pcapng_tsc_to_ns(uint64_t cycles) > > > > } > > > > } > > > > > > > > - return pcapng_time.ns + rte_reciprocal_divide_u64(delta * > > > > NSEC_PER_SEC, > > > > - > > > > &pcapng_time.tsc_hz_inverse); > > > > + return pcapng_time.ns + rte_reciprocal_divide_u64(delta, > > > > + > > > > &pcapng_time.tsc_hz_inverse) * NSEC_PER_SEC; > > > > } > > This is less accurate. The TSC (CPU clock frequency) is not necessarily > an even multiple of nanoseconds. > > If you want to send patches please follow the contributing guidelines > and run checkpatch on them.
Yeah, I realized that and tried to improve on it by dividing by less at init and multiplying by less at run time. However I noticed another problem with my patches, that there is a time gap that keeps growing for some reason, and I can't figure out what's wrong. I'll try some more and will gladly test anything proposed. Thanks!
