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Date: Thu, 06 Jun 2013 07:28:06 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc: Jesper Dangaard Brouer <brouer@...hat.com>,
Stephen Hemminger <stephen@...workplumber.org>,
David Miller <davem@...hat.com>, j.vimal@...il.com,
Michal Soltys <soltys@....info>,
Mike Frysinger <vapier@...too.org>,
Jussi Kivilinna <jussi.kivilinna@...et.fi>,
Patrick McHardy <kaber@...sh.net>,
Jiri Pirko <jpirko@...hat.com>,
Toke Høiland-Jørgensen <toke@...e.dk>,
Dave Taht <dave.taht@...il.com>, netdev@...r.kernel.org,
bloat@...ts.bufferbloat.net, Dan Siemon <dan@...erfire.com>,
Jim Gettys <jg@...edesktop.org>,
Steven Barth <cyrus@...nwrt.org>, Felix Fietkau <nbd@....name>,
Jiri Benc <jbenc@...hat.com>
Subject: Re: RFC: Proposed fix for tc linklayer calc broken after commit
56b765b79 (htb: improved accuracy at high rates)
On Thu, 2013-06-06 at 15:55 +0200, Jesper Dangaard Brouer wrote:
> Requesting comments.
>
> So, bacically commit 56b765b79 (htb: improved accuracy at high rates),
> broke the "linklayer atm" handling. As it didn't update the iproute tc util.
>
> Treating this as a regression fix, this is the smallest and least
> intrusive solution I could come up with.
>
> I'm basically restoring the "linklayer atm" handling, by using the
> __reserved field in struct tc_ratespec, to convey the chosen
> linklayer option.
>
>
> KERNEL patch:
> =============
>
> [PATCH RFC] net_sched: restore "linklayer atm" handling
>
> From: Jesper Dangaard Brouer <brouer@...hat.com>
>
> commit 56b765b79 ("htb: improved accuracy at high rates")
> broke the "linklayer atm" handling.
>
> tc class add ... htb rate X ceil Y linklayer atm
>
> This patch restores the "linklayer atm" handling, by using the
> __reserved field in struct tc_ratespec, to convey the choosen
> linklayer option.
>
> This requires a corrosponding iproute2 tc fix, that updates this
> field. Older tc binaries can be detected by the kernel, as the
> field would be zero.
>
> Request-For-Comments-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>
> include/net/sch_generic.h | 8 +++++++-
> include/uapi/linux/pkt_sched.h | 11 ++++++++++-
> net/sched/sch_generic.c | 4 ++++
> 3 files changed, 21 insertions(+), 2 deletions(-)
>
>
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index e7f4e21..c9916b1 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -682,13 +682,18 @@ struct psched_ratecfg {
> u64 rate_bps;
> u32 mult;
> u16 overhead;
> + u8 linklayer;
> u8 shift;
> };
>
> static inline u64 psched_l2t_ns(const struct psched_ratecfg *r,
> unsigned int len)
> {
> - return ((u64)(len + r->overhead) * r->mult) >> r->shift;
> + u64 pkt_len = len + r->overhead;
> +
> + if (r->linklayer == TC_LINKLAYER_ATM)
> + pkt_len = DIV_ROUND_UP(pkt_len,48)*53;
Is this working on 32bit kernel ?
> + return (pkt_len * r->mult) >> r->shift;
> }
I have no idea why you include so many people on your mails.
This looks like ATM link have real rate of 48/53 of the rate.
Since we have to distribute a new tc version, why not doing
"tc ... rate rate X ceil Y linklayer atm"
->
"tc ... rate X*48/53 Y*48/53"
It avoids hard coded values in the kernel.
Or make it use STAB if people really want to count bits/cells instead of
bytes.
Lets try to keep this overhead out of the fast path.
--
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