From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Hagood <david.hagood@gmail.com>
Subject: Re: Usefulness of xt_recent's "last seen" and "oldest_pkt" on a tickless
 system
Date: Sun, 11 Jan 2015 17:24:11 -0600
Message-ID: <54B3061B.5000503@gmail.com>
References: <alpine.LSU.2.11.1501111106300.616@nerf60.vanv.qr> <54B29C5A.3010708@gmail.com> <alpine.LSU.2.11.1501111925200.24030@nerf60.vanv.qr>
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To: Jan Engelhardt <jengelh@inai.de>
Cc: Netfilter user mailing list <netfilter@vger.kernel.org>

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.