Messages in this thread | | | From | Willem de Bruijn <> | Date | Mon, 17 Jun 2019 16:20:12 -0400 | Subject | Re: [PATCH net v4] net/udp_gso: Allow TX timestamp with UDP GSO |
| |
On Mon, Jun 17, 2019 at 3:05 PM Fred Klassen <fklassen@appneta.com> wrote: > > Fixes an issue where TX Timestamps are not arriving on the error queue > when UDP_SEGMENT CMSG type is combined with CMSG type SO_TIMESTAMPING. > This can be illustrated with an updated updgso_bench_tx program which > includes the '-T' option to test for this condition. It also introduces > the '-P' option which will call poll() before reading the error queue. > > ./udpgso_bench_tx -4ucTPv -S 1472 -l2 -D 172.16.120.18 > poll timeout > udp tx: 0 MB/s 1 calls/s 1 msg/s > > The "poll timeout" message above indicates that TX timestamp never > arrived. > > This patch preserves tx_flags for the first UDP GSO segment. Only the > first segment is timestamped, even though in some cases there may be > benefital in timestamping both the first and last segment. > > Factors in deciding on first segment timestamp only: > > - Timestamping both first and last segmented is not feasible. Hardware > can only have one outstanding TS request at a time. > > - Timestamping last segment may under report network latency of the > previous segments. Even though the doorbell is suppressed, the ring > producer counter has been incremented. > > - Timestamping the first segment has the upside in that it reports > timestamps from the application's view, e.g. RTT. > > - Timestamping the first segment has the downside that it may > underreport tx host network latency. It appears that we have to pick > one or the other. And possibly follow-up with a config flag to choose > behavior. > > v2: Remove tests as noted by Willem de Bruijn <willemb@google.com> > Moving tests from net to net-next > > v3: Update only relevant tx_flag bits as per > Willem de Bruijn <willemb@google.com> > > v4: Update comments and commit message as per > Willem de Bruijn <willemb@google.com> > > Fixes: ee80d1ebe5ba ("udp: add udp gso") > Signed-off-by: Fred Klassen <fklassen@appneta.com>
Acked-by: Willem de Bruijn <willemb@google.com>
| |