netdev - Re: [PATCH iproute2] Re: HTB accuracy for high speed

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Message-ID: <20090529134956.44104655@nehalam>
Date:	Fri, 29 May 2009 13:49:56 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Antonio Almeida <vexwek@...il.com>, netdev@...r.kernel.org,
	kaber@...sh.net, davem@...emloft.net, devik@....cz,
	Eric Dumazet <dada1@...mosbay.com>,
	Vladimir Ivashchenko <hazard@...ncoudi.com>
Subject: Re: [PATCH iproute2] Re: HTB accuracy for high speed

On Fri, 29 May 2009 21:46:43 +0200
Jarek Poplawski <jarkao2@...il.com> wrote:

> On Fri, May 29, 2009 at 06:02:39PM +0100, Antonio Almeida wrote:
> > On Thu, May 28, 2009 at 10:12 PM, Jarek Poplawski wrote:
> > > Yes, but according to my assessment there should be "only" 50Mbit
> > > difference for this rate/packet size. Anyway, could you try a testing
> > > patch below, which should add some granularity to this rate table?
> > >
> > > Thanks,
> > > Jarek P.
> > > ---
> > >
> > >  include/net/pkt_sched.h |    4 ++--
> > >  1 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/net/pkt_sched.h b/include/net/pkt_sched.h
> > > index e37fe31..f0faf03 100644
> > > --- a/include/net/pkt_sched.h
> > > +++ b/include/net/pkt_sched.h
> > > @@ -42,8 +42,8 @@ typedef u64   psched_time_t;
> > >  typedef long   psched_tdiff_t;
> > >
> > >  /* Avoid doing 64 bit divide by 1000 */
> > > -#define PSCHED_US2NS(x)                        ((s64)(x) << 10)
> > > -#define PSCHED_NS2US(x)                        ((x) >> 10)
> > > +#define PSCHED_US2NS(x)                        ((s64)(x) << 6)
> > > +#define PSCHED_NS2US(x)                        ((x) >> 6)
> > >
> > >  #define PSCHED_TICKS_PER_SEC           PSCHED_NS2US(NSEC_PER_SEC)
> > >  #define PSCHED_PASTPERFECT             0
> > 
> > It's better! This patch gives more accuracy to HTB. Here some values:
> > Note that these are boundary values, so, e.g., any HTB configuration
> > between 377000Kbit and 400000Kbit would fall in the same step - close
> > to 397977Kbit.
> 
> Good news! So it seems there are no other reasons of this inaccuracy
> than too coarse granularity, but I have to check this yet. Alas there
> is needed something more than this patch, because it probably breaks
> other things like hfsc.
> 
> Thanks,
> Jarek P.
> 

Why would it break hfsc, if it isn't already broken.
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