That's within reason given that thread time offsets are not recalculated immediately, and that (for stability reasons) the clock-rate update algorithm uses exponential smoothing.
Aside from accounting for the issue in your code, there probably isn't much to be done about it... D -----Original Message----- From: Prashant Upadhyaya <praupadhy...@gmail.com> Sent: Monday, June 15, 2020 8:58 AM To: Dave Barach (dbarach) <dbar...@cisco.com> Cc: vpp-dev@lists.fd.io Subject: Re: [vpp-dev] Regarding vlib_time_now Hi Dave, Thanks, on a VM I am observing the reduction from a couple of microseconds to 50 microseconds at times NTP was turned on. After turning it off, I don't see the time reduction. The output of the command is below vppctl show clock verbose Time now 16712.719968, reftime 16712.719967, error .000001, clocks/sec 2596982853.770165 Time last barrier release 16709.938950671 1: Time now 16710.417730, reftime 16710.417730, error 0.000000, clocks/sec 2596982875.038256 Thread 1 offset 2.302279669 error -.000000032 [root@bfs-dl360g9-16-vm4 iptabl]# /opt/opwv/integra/SystemActivePath/tools/vpp/bin/vppctl show clock verbose Time now 16715.621101, reftime 16715.621101, error 0.000000, clocks/sec 2596982853.770165 Time last barrier release 16712.721636492 1: Time now 16713.318854, reftime 16713.318854, error 0.000000, clocks/sec 2596982875.038256 Thread 1 offset 2.302279482 error -.000000008 [root@bfs-dl360g9-16-vm4 iptabl]# /opt/opwv/integra/SystemActivePath/tools/vpp/bin/vppctl show clock verbose Time now 16718.249427, reftime 16718.249427, error 0.000000, clocks/sec 2596982853.770165 Time last barrier release 16715.621212275 1: Time now 16715.947179, reftime 16715.947179, error 0.000000, clocks/sec 2596982875.038256 Thread 1 offset 2.302279562 error -.000000008 [root@bfs-dl360g9-16-vm4 iptabl]# /opt/opwv/integra/SystemActivePath/tools/vpp/bin/vppctl show clock verbose Time now 16719.646461, reftime 16719.646461, error 0.000000, clocks/sec 2596982853.770165 Time last barrier release 16718.249525477 1: Time now 16717.344206, reftime 16717.344206, error 0.000000, clocks/sec 2596982875.038256 Thread 1 offset 2.302279598 error -.000000009 [root@bfs-dl360g9-16-vm4 iptabl]# /opt/opwv/integra/SystemActivePath/tools/vpp/bin/vppctl show clock verbose Time now 16721.162232, reftime 16721.162232, error 0.000000, clocks/sec 2596982853.770165 Time last barrier release 16720.702629716 1: Time now 16718.859979, reftime 16718.859979, error 0.000000, clocks/sec 2596982875.038256 Thread 1 offset 2.302279598 error -.000000008 [root@bfs-dl360g9-16-vm4 iptabl]# /opt/opwv/integra/SystemActivePath/tools/vpp/bin/vppctl show clock verbose Time now 16722.313997, reftime 16722.313997, error 0.000000, clocks/sec 2596982853.770165 Time last barrier release 16721.162470894 1: Time now 16720.011753, reftime 16720.011753, error 0.000000, clocks/sec 2596982875.038256 Thread 1 offset 2.302279597 error -.000000009 Regards -Prashant On Sun, Jun 14, 2020 at 8:12 PM Dave Barach (dbarach) <dbar...@cisco.com> wrote: > > What is the magnitude of the delta that you observe? What does "show clock > verbose" say about the state of clock-rate convergence? Is a deus ex machina > (e.g. NTP) involved? > > > > -----Original Message----- > From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> On Behalf Of Prashant > Upadhyaya > Sent: Sunday, June 14, 2020 10:32 AM > To: vpp-dev@lists.fd.io > Subject: [vpp-dev] Regarding vlib_time_now > > > > Hi, > > > > I am using VPP 19.08 > > In my worker threads, I am observing that when I am making successive calls > to vlib_time_now in a polling node, sometimes the value of the time reduces. > > Is this expected to happen ? (presumably because of the implementation which > tries to align the times in workers ?) I have an implementation which is > extremely sensitive to time at microsecond level and depends on the the > vlib_time_now only increasing monotonically across calls individually in the > workers (or remain the same but never decrease) on a per worker basis even if > the times within the workers are not synchronized. > > > > Regards > > -Prashant
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