netdev - Re: [PATCH] net: make tc-police action MTU behavior match documentation

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Message-ID: <MWHPR12MB1344DB0C462CBBEE8BEB6CADDDC00@MWHPR12MB1344.namprd12.prod.outlook.com>
Date:   Tue, 27 Feb 2018 17:41:48 +0000
From:   Andrew Collins <acollins@...dlepoint.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     Jamal Hadi Salim <jhs@...atatu.com>,
        David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: make tc-police action MTU behavior match
 documentation

> I don't find such statement from the man page:
> http://man7.org/linux/man-pages/man8/tc-police.8.html

> What am I missing?

Under MTU the man page states:

mtu BYTES[/BYTES]
              This is the maximum packet size handled by the policer (larger ones will be handled like they exceeded the configured rate). Setting this value correctly will improve the scheduler's precision.   
              Value  formatting  is identical to burst above. ->Defaults to unlimited<-.

Peakrate requiring MTU isn't mentioned directly in the man page, but if you provide peakrate without MTU, tc complains:

"mtu" is required, if "peakrate" is requested.

The idea here is just to make the actual implementation match these two statements, MTU is unlimited, unless you use peakrate in which case you have to provide it (although if you craft netlink messages without tc you can set peakrate with no mtu, and the action will still default to a reasonable mtu rather than falling over).

Andrew Collins