TBF man page: peakrate must be greater than rate

TBF man page: peakrate must be greater than rate

[Andy Walker]

Hi,

I was struggling with the following command line:
tc qdisc add dev eth1 parent 1:1 handle 10: tbf rate 10.0kbit maxburst
10kb latency 50ms peakrate 10kbit mtu 1600
RTNETLINK answers: Invalid argument

When I altered peakrate to be 10.1kbit, tbf accepted its parameters.

Looking in dmesg, I found the following:

sch_tbf: peakrate 1250 is lower than or equals to rate 1250

The man page does not specify that peakrate needs to be greater than
rate. This would probably be a useful addition, as it's easy to assume
that the two can/should be set to the same value for precise rate
limiting.

Thanks,
Andy

Re: TBF man page: peakrate must be greater than rate

[Stephen Hemminger]

On Fri, 3 Sep 2021 16:48:45 +0100
Andy Walker <camtarn@camtarn.org> wrote:

> Hi,
> 
> I was struggling with the following command line:
> tc qdisc add dev eth1 parent 1:1 handle 10: tbf rate 10.0kbit maxburst
> 10kb latency 50ms peakrate 10kbit mtu 1600
> RTNETLINK answers: Invalid argument
> 
> When I altered peakrate to be 10.1kbit, tbf accepted its parameters.
> 
> Looking in dmesg, I found the following:
> 
> sch_tbf: peakrate 1250 is lower than or equals to rate 1250
> 
> The man page does not specify that peakrate needs to be greater than
> rate. This would probably be a useful addition, as it's easy to assume
> that the two can/should be set to the same value for precise rate
> limiting.
> 
> Thanks,
> Andy

The kernel should be reporting error message via netlink extack
but it isn't.  Anytime user has to look in dmesg to see an error
it is bad.

TBF is old and rarely modified code in the kernel. It looks like
it could use some attention.

Re: TBF man page: peakrate must be greater than rate

[Stephen Hemminger]

On Fri, 3 Sep 2021 16:48:45 +0100
Andy Walker <camtarn@camtarn.org> wrote:

> Hi,
> 
> I was struggling with the following command line:
> tc qdisc add dev eth1 parent 1:1 handle 10: tbf rate 10.0kbit maxburst
> 10kb latency 50ms peakrate 10kbit mtu 1600
> RTNETLINK answers: Invalid argument
> 
> When I altered peakrate to be 10.1kbit, tbf accepted its parameters.
> 
> Looking in dmesg, I found the following:
> 
> sch_tbf: peakrate 1250 is lower than or equals to rate 1250
> 
> The man page does not specify that peakrate needs to be greater than
> rate. This would probably be a useful addition, as it's easy to assume
> that the two can/should be set to the same value for precise rate
> limiting.
> 
> Thanks,
> Andy

Try this:

From 20f4d28336fd7b1de2df1a7478319f44b3e258e2 Mon Sep 17 00:00:00 2001
From: Stephen Hemminger <sthemmin@microsoft.com>
Date: Fri, 3 Sep 2021 09:24:52 -0700
Subject: [PATCH] net: sched: tbf replace log message with extack

The Token Bucket Filter qdisc should be using extack
to report errors, rather than forcing user to look in
dmesg.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 net/sched/sch_tbf.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
index 78e79029dc63..33cd712caea5 100644
--- a/net/sched/sch_tbf.c
+++ b/net/sched/sch_tbf.c
@@ -387,8 +387,7 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt,
 			prate64 = nla_get_u64(tb[TCA_TBF_PRATE64]);
 		psched_ratecfg_precompute(&peak, &qopt->peakrate, prate64);
 		if (peak.rate_bytes_ps <= rate.rate_bytes_ps) {
-			pr_warn_ratelimited("sch_tbf: peakrate %llu is lower than or equals to rate %llu !\n",
-					peak.rate_bytes_ps, rate.rate_bytes_ps);
+			NL_SET_ERR_MSG(extack, "peakrate is lower than or equals to rate");
 			err = -EINVAL;
 			goto done;
 		}
@@ -405,9 +404,7 @@ static int tbf_change(struct Qdisc *sch, struct nlattr *opt,
 	}
 
 	if (max_size < psched_mtu(qdisc_dev(sch)))
-		pr_warn_ratelimited("sch_tbf: burst %llu is lower than device %s mtu (%u) !\n",
-				    max_size, qdisc_dev(sch)->name,
-				    psched_mtu(qdisc_dev(sch)));
+		NL_SET_ERR_MSG(extack, "burst is lower than device mtu");
 
 	if (!max_size) {
 		err = -EINVAL;
-- 
2.30.2