On Wed, Jun 27, 2018 at 1:17 PM, Yann Droneaud <ydroneaud@xxxxxxxxxx> 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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