kern/189720: [ipfw] [patch] pps action for ipfw

['Luigi Rizzo']

The following reply was made to PR kern/189720; it has been noted by GNATS.

From: 'Luigi Rizzo' <rizzo at iet.unipi.it>
To: bycn82 <bycn82 at gmail.com>
Cc: bug-followup at FreeBSD.org
Subject: Re: kern/189720: [ipfw] [patch] pps action for ipfw
Date: Thu, 29 May 2014 17:17:59 +0200

 On Thu, May 29, 2014 at 11:06:27PM +0800, bycn82 wrote:
 > 
 > 
 > -----Original Message-----
 > From: Luigi Rizzo [mailto:rizzo at iet.unipi.it] 
 > Sent: 29 May, 2014 22:12
 > To: bug-followup at FreeBSD.org; bycn82 at gmail.com
 > Subject: kern/189720: [ipfw] [patch] pps action for ipfw
 > 
 > Hi,
 > I have looked at the update from May 13th but it is not ready yet, the code assumes HZ=1000 so 1 tick=1ms.
 > 
 > The translation can be done in userspace or in the kernel.
 > I would prefer the latter.
 > I see, 
 > If the HZ=3, that means every tick=333ms
 > And if the user wants to ??? 1 packet per 500ms???, then in the backend will not do the exactly the same as what user expect.
 > 
 > Actually the implementation should be ???packets per ticks???, so how about this? Instead of translate it in codes. Why not update the document, and explain it to the user in the document ?
 
 'Packets per tick' this is not a useful specification
 since the tick's duration is unknown to the user.
 Depending on the platform you can have HZ ranging from 15-20 (on windows)
 to 10000 or even more. Normal values are 100, 250, 1000 but
 you just cannot know what you are going to get.
 
 Yes there are rounding issues, and yes it is boring to write
 code to handle them.
 
 luigi