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

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Date:	Fri, 29 May 2009 10:28:45 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Antonio Almeida <vexwek@...il.com>
Cc:	Jarek Poplawski <jarkao2@...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 18:02:39 +0100
Antonio Almeida <vexwek@...il.com> 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.
> This test was made over the same conditions: generating 950Mbit/s of
> unidirectional tcp traffic of 800 bytes packets long.

You really need to get a better box than the dual core AMD.
There is only millisecond (or worse with HZ=100) resolution possible because
there is no working TSC on that hardware.


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