Hi Dave, I am seeing this with VPP 21.01. Yes NTP is on and the print starts filling up the log. I see fixes made in this area in time.h and time.c addressing the algorithm. Questions: 1. "Vpp has to continuously adjust its idea of the current clock rate" -- How long could this be? Seconds, minutes or hours? 2. Is the warning suggesting a problem (with few expected failures around this event that rely on timers) or information displayed to the user that the clock rate is being adjusted? What is the outcome expected with entities of the system relying on timers whenever this happens?
Thanks, Prashant On Fri, Aug 6, 2021 at 5:08 AM Dave Barach <v...@barachs.net> wrote: > Which version of vpp are you running? Which Linux kernel is involved? What > kind of hardware? Lastly, did you just start running NTP on the system? > > > > Yes, of course it means something: every N seconds, vpp calculates its > idea of the current clock frequency by asking the kernel [via the > clock_gettime ( CLOCK_REALTIME) syscall] what time it is. It asks the CPU > for the current clock tick [on x86_64, via “RDTSC”]. Some arithmetic later, > we have a new clock rate for the processor. > > > > We can’t simply believe the new clock rate, because e.g. NTP > synchronization can change the kernel reference clock by *minutes* or > *hours*. Every timer in the system breaks catastrophically if vpp’s idea > of the CPU clock rate is seriously wrong. After a suitable number of > experiments, we decided to reject frequency changes of more than one > percent. > > > > Vpp has to continuously adjust its idea of the current clock rate, > otherwise long-running timers won’t be accurate enough. > > > > > > See .../src/vppinfra/time.c:clib_time_verify_frequency() and > .../src/vppinfra/time.h:clib_time_now_internal() for details. > > > > *From:* vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> *On Behalf Of *Gudimetla, > Leela Sankar via lists.fd.io > *Sent:* Thursday, August 5, 2021 11:31 PM > *To:* vpp-dev@lists.fd.io > *Subject:* [vpp-dev] Rejecting large frequency change > > > > Hello, > > > > We have started seeing the below warning message coming continuously. > Traffic is running on several vhost-ports and physical ports. These > messages are coming even after a restart with a slow rate. > > VPP clib_warning: clib_time_verify_frequency:248: Rejecting large > frequency change of 1.01% > > > > Does this mean something ? > > > > Thanks, > > Leela sankar > > > >
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