Date: Fri, 30 May 2014 22:39:37 +0800 From: Julian Elischer <julian@freebsd.org> To: bycn82 <bycn82@gmail.com>, "'Luigi Rizzo'" <rizzo@iet.unipi.it>, freebsd-ipfw@FreeBSD.org Subject: Re: kern/189720: [ipfw] [patch] pps action for ipfw Message-ID: <53889829.6030307@freebsd.org> In-Reply-To: <007f01cf7b52$efd8a0c0$cf89e240$@gmail.com> References: <201405291520.s4TFK124032925@freefall.freebsd.org> <007f01cf7b52$efd8a0c0$cf89e240$@gmail.com>
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On 5/29/14, 11:30 PM, bycn82 wrote: > I got it, > > if the HZ=3, it always cannot meet the " 1 packet per 500ms" perfectly. > But if we to "X packet per Y ticks", actually the result is the same, still cannot meet the "1 packet per 500 ms" perfectly, instead, the "packet per Y ticks" will force user to use " X packet per Y*300 ms". And the user need to understand how many millisecond each tick is . on e can write an implementation that notes how much the calculation was off by for each tick and corrects the number for the next tick.. e.g. with Hz=10, 8pps should give sometimes 1ppt and sometimes 0ppt but a simple calculation will always give 0 every tick so you need to have some way of carrying forward 'unused bandwidth' so that teh calculation looks like (over a second) ppt(real) ppt(int) 0.8 (0) 0.8+0.8=1.6 (1) 0.6+0.8=1.4 (1) (subtract 1 from 1.6, and then add the 0.8 per tick) 0.4+0.8=1.2 (1) 0.2+0.8=1.0 (1) 0.0+0.8=0.8(0) (sequence repeats) 0.8+0.8=1.6 (1) 0.6+0.8=1.4 (1) 0.4+0.8=1.2 (1) 0.2+0.8=1.0 (1) 0.0+0.8=0.8(0) if you use any of the the int(ppt) in a tick you subtract the amount used. if not you allow it to build, up to some maximum value. (sequence repeats) 0.8+0.8=1.6 (1) (not used) 1.6+0.8=2.4 (2) (not used) 2.4+0.8=3.2 (3) (not used) 3.2+0.8=4.0 (4) (4 packets allowed through further packets held or dropped) 0.0+0.8=0.8(0) 0.8+0.8=1.6 (1) (not used) 1.6+0.8=2.4 (2) (not used) 2.4+0.8=3.2 (3) 1 packet used.. 1.0 subtracted 2.2+0.8=3.0 (4) (4 packets allowed through further packets held or dropped) 0.0+0.8=0.8(0) etc. one does this with some form of fixed point arithmetic as floating point isn't used in the kernel. > So I will update it this weekend. > > >> -----Original Message----- >> From: owner-freebsd-ipfw@freebsd.org [mailto:owner-freebsd- >> ipfw@freebsd.org] On Behalf Of 'Luigi Rizzo' >> Sent: 29 May, 2014 23:20 >> To: freebsd-ipfw@FreeBSD.org >> Subject: Re: kern/189720: [ipfw] [patch] pps action for ipfw >> >> The following reply was made to PR kern/189720; it has been noted by >> GNATS. >> >> From: 'Luigi Rizzo' <rizzo@iet.unipi.it> >> To: bycn82 <bycn82@gmail.com> >> Cc: bug-followup@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@iet.unipi.it] > Sent: 29 May, 2014 22:12 > To: >> bug-followup@FreeBSD.org; bycn82@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 >> _______________________________________________ >> freebsd-ipfw@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-ipfw >> To unsubscribe, send any mail to "freebsd-ipfw-unsubscribe@freebsd.org" > _______________________________________________ > freebsd-ipfw@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-ipfw > To unsubscribe, send any mail to "freebsd-ipfw-unsubscribe@freebsd.org" >
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