On Wed, Jun 27, 2018 at 1:17 PM, Yann Droneaud <ydrone...@opteya.com> wrote:
> Hi, > > Le mardi 26 juin 2018 à 19:44 +0530, Subhashini Rao Beerisetty a > écrit : > > > > In the kernel code I see it supports CLOCK_REALTIME \ CLOCK_MONOTONIC > > \ CLOCK_MONOTONIC_RAW timestamps. Can someone explain what’s major > > difference between those three modes and when to use which one? > > > > A generic answer could be found here: > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/time.h.html > > > I’ve N number of Linux machines in the network with the same software > > running. Basically I need to collect the timestamps in kernel mode in > > all the machines and then compare, which(either CLOCK_REALTIME or > > CLOCK_MONOTIC_RAW or MONOTONIC) one would be the correct way? > > > > Probably none. Anyway, please find some hints below: > > None of the monotonic clocks can be used because they're not supposed > to be synchronized accross the network > > You're left with CLOCK_REALTIME, which is not synchronized accross the > network by default. > Does printk log timestamp by default uses the CLOCK_REALTIME? > > So before doing timestamp comparison, you would need to setup time > synchronisation between hosts on your network: NTP to synchronise hosts > to the same seconds with couple of millisecond precision, PTP for sub > millisecond precision. > Can you point me on how to setup time synchronisation between hosts on network. > > Time synchronisation is a tough problem but it's required if you want > to be able to compare timestamp accross hosts in a network. > > Regards. > > -- > Yann Droneaud > OPTEYA > >
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