Re: Usefulness of xt_recent's "last seen" and "oldest_pkt" on a tickless system

[David Hagood <david.hagood@gmail.com>]

On 01/11/2015 12:49 PM, Jan Engelhardt wrote:
> The jifs/sec is set by CONFIG_HZ, for which a common kernel only
> offers the compile-time choices of 100, 250, 300, 1000, not 2150.
> If you find a value of 2150, you are probably looking at the wrong
> value, or have a heavily modified custom kernel.
Nope. Standard Ubuntu 14.04 low latency kernel. And the value is 
computed by looking at the btime field in /proc/timer_list (not 
/proc/stat - my bad). Moreover, I can tell by causing a packet to be 
logged at a known time in a xt_recent rule, looking at the last_seen 
field, and then computing the ratio of the known time expressed as 
seconds since boot, and in jiffies from the kernel.

>
> TTBONK, there is no reliable way for userspace to tell the value of
> CONFIG_HZ, so yes, _showing_ jiffies in /proc/net/xt_recent is
> useless - but at least you can compare the numbers against each other
> (not that that seems useful, either).
>

Agreed.