* [LARTC] Re: CBQ and all other qdiscs now REALLY completely documented (almost!)
@ 2001-12-08 23:23 bert hubert
2001-12-09 1:30 ` bert hubert
0 siblings, 1 reply; 2+ messages in thread
From: bert hubert @ 2001-12-08 23:23 UTC (permalink / raw)
To: lartc
On Sat, Dec 08, 2001 at 02:20:20PM -0500, jamal wrote:
> Linux remaps packets incoming with different values to some internal
> value; the colum "mapped to" shows the internal mapping
>
> 8value(hex) TOS(dec) mapped to(dec)
> ----------------------------------
> 0x0 0 0
> 1 7
> 2 0
> 3 0
> 4 2
> 5 2
> 6 2
> 7 2
> 0x10 8 6
> 9 6
> 10 6
> 11 6
> 12 2
> 13 2
> 14 2
> 15 2
I find this tos2prio table in the kernel (2.5.x), which is somewhat
different than your table:
0 TC_PRIO_BESTEFFORT, 0
1 TC_PRIO_(FILLER), 1
2 TC_PRIO_BESTEFFORT, 0
3 TC_PRIO_(BESTEFFORT), 0
4 TC_PRIO_BULK, 2
5 TC_PRIO_(BULK), 2
6 TC_PRIO_BULK, 2
7 TC_PRIO_(BULK), 2
8 TC_PRIO_INTERACTIVE, 6
9 TC_PRIO_(INTERACTIVE), 6
10 TC_PRIO_INTERACTIVE, 6
11 TC_PRIO_(INTERACTIVE), 6
12 TC_PRIO_INTERACTIVE_BULK, 4
13 TC_PRIO_(INTERACTIVE_BULK), 4
14 TC_PRIO_INTERACTIVE_BULK, 4
15 TC_PRIO_(INTERACTIVE_BULK) 4
> Fill in the "8value(hex)" column gaps using the bitmap from RFC1349 for
> the 8 bits; These are the values ou would see with tcpdump -vvv
> I filled the two easiest ones i could compute in my head.
>
> Second step:
>
> Take the default priority map:
> 1, 2, 2, 2, 1, 2, 0, 0 , 1, 1, 1, 1, 1, 1, 1, 1
> This applies for both default prio and the 3-band FIFO queue.
> Note the queue map fitted on the last column
>
> 8 but value TOS mapped to queue map
> ---------------------------------------------
> 0x0 0 0 1
> 1 7 2
> 2 0 2
> 3 0 2
> 4 2 1
> 5 2 2
> 6 2 0
> 7 2 0
> 0x10 8 6 1
> 9 6 1
> 10 6 1
> 11 6 1
> 12 2 1
> 13 2 1
> 14 2 1
> 15 2 1
I've changed this table to:
TOS Bits Means Linux Priority Band
------------------------------------------------------------
0x0 0 Normal Service 0 Best Effort 1
0x2 1 Minimize Monetary Cost 1 Filler 2
0x4 2 Maximize Reliability 0 Best Effort 1
0x6 3 mmc+mr 0 Best Effort 1
0x8 4 Maximize Throughput 2 Bulk 2
0xa 5 mmc+mt 2 Bulk 2
0xc 6 mr+mt 2 Bulk 2
0xe 7 mmc+mr+mt 2 Bulk 2
0x10 8 Minimize Delay 6 Interactive 0
0x12 9 mmc+md 6 Interactive 0
0x14 10 mr+md 6 Interactive 0
0x16 11 mmc+mr+md 6 Interactive 0
0x18 12 mt+md 4 Int. Bulk 1
0x1a 13 mmc+mt+md 4 Int. Bulk 1
0x1c 14 mr+mt+md 4 Int. Bulk 1
0x1e 15 mmc+mr+mt+md 4 Int. Bulk 1
http://ds9a.nl/lartc/HOWTO/cvs/2.4routing/output/2.4routing-9.html#ss9.2
Your table appears to imply that a Maximum Reliability, Mininum Delay
packet, TOS bits=9, gets mapped to band 1, not 0, which would not make
sense.
Laying it out like this, which does appear how it works, does mean that you
can specify priorities in the priomap which do not correspond to possible
TOS values.
Is it possible at all to set skb->priority from userspace without going
through the tos2prio mapping?
CBQ can use the skb->priority to classify:
/*
* Step 1. If skb->priority points to one of our classes, use it.
*/
if (TC_H_MAJ(prio^sch->handle) = 0 &&
(cl = cbq_class_lookup(q, prio)) != NULL)
return cl;
But to do this, you would need to be able to set skb->priority to a 32bit
number:
include/linux/pkt_sched.h:#define TC_H_MAJ_MASK (0xFFFF0000U)
include/linux/pkt_sched.h:#define TC_H_MAJ(h) ((h)&TC_H_MAJ_MASK)
I can't find where you would do this, any clues?
Thanks again for taking the time to help me.
Regards,
bert
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* [LARTC] Re: CBQ and all other qdiscs now REALLY completely documented (almost!)
2001-12-08 23:23 [LARTC] Re: CBQ and all other qdiscs now REALLY completely documented (almost!) bert hubert
@ 2001-12-09 1:30 ` bert hubert
0 siblings, 0 replies; 2+ messages in thread
From: bert hubert @ 2001-12-09 1:30 UTC (permalink / raw)
To: lartc
On Sat, Dec 08, 2001 at 08:14:10PM -0500, jamal wrote:
> Yes, sorry the last 4 are int_bulk (value 4) and not just bulk (2). good
> eye. You are still abusing the word TOS. Thats only 4 bits not 8;
> Use the terminology from RFC1349 at least.
Will do.
> > http://ds9a.nl/lartc/HOWTO/cvs/2.4routing/output/2.4routing-9.html#ss9.2
> >
> > Your table appears to imply that a Maximum Reliability, Mininum Delay
> > packet, TOS bits=9, gets mapped to band 1, not 0, which would not make
> > sense.
>
> This is the priomap: 1, 2, 2, 2, 1, 2, 0, 0 , 1, 1, 1, 1, 1, 1, 1, 1
> It says 1 is the right value
AFAICT, the priomap maps skb->priority to band. So the translation is as
follows:
Type of Service octet, which is fed to:
skb->priority = rt_tos2priority(iph->tos);
To extract the four TOS bits, and to translate to prio:
static inline char rt_tos2priority(u8 tos)
{
return ip_tos2prio[IPTOS_TOS(tos)>>1];
}
----
__u8 ip_tos2prio[16] = {
TC_PRIO_BESTEFFORT,
ECN_OR_COST(FILLER),
TC_PRIO_BESTEFFORT,
ECN_OR_COST(BESTEFFORT),
TC_PRIO_BULK,
ECN_OR_COST(BULK),
TC_PRIO_BULK,
ECN_OR_COST(BULK),
TC_PRIO_INTERACTIVE,
ECN_OR_COST(INTERACTIVE),
TC_PRIO_INTERACTIVE,
ECN_OR_COST(INTERACTIVE),
TC_PRIO_INTERACTIVE_BULK,
ECN_OR_COST(INTERACTIVE_BULK),
TC_PRIO_INTERACTIVE_BULK,
ECN_OR_COST(INTERACTIVE_BULK)
};
---
#define TC_PRIO_BESTEFFORT 0
#define TC_PRIO_FILLER 1
#define TC_PRIO_BULK 2
#define TC_PRIO_INTERACTIVE_BULK 4
#define TC_PRIO_INTERACTIVE 6
#define TC_PRIO_CONTROL 7
#define TC_PRIO_MAX 15
net/sched/sched_generic.c:
static const u8 prio2band[TC_PRIO_MAX+1] { 1, 2, 2, 2, 1, 2, 0, 0 , 1, 1, 1, 1, 1, 1, 1, 1 };
list = ((struct sk_buff_head*)qdisc->data) +
prio2band[skb->priority&TC_PRIO_MAX];
> > CBQ can use the skb->priority to classify:
>
> so do prio and pfifo_fast (as i am sure you are aware)
Of course, but only CBQ (& HTB, by the way) can extract a classid directly
from it, without a priomap. Devik is planning to learn HTB to extract a
classid directly from the fwmark, to skip a layer of indirection.
Regards,
bert hubert
--
http://www.PowerDNS.com Versatile DNS Software & Services
Trilab The Technology People
Netherlabs BV / Rent-a-Nerd.nl - Nerd Available -
'SYN! .. SYN|ACK! .. ACK!' - the mating call of the internet
_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://ds9a.nl/lartc/
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2001-12-08 23:23 [LARTC] Re: CBQ and all other qdiscs now REALLY completely documented (almost!) bert hubert
2001-12-09 1:30 ` bert hubert
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