netdev - Re: Validation of forward

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Date:   Wed, 3 Jul 2019 00:19:31 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        bridge@...ts.linux-foundation.org, netdev <netdev@...r.kernel.org>
Subject: Re: Validation of forward_delay seems wrong...

On 02/07/2019 23:47, Andrew Lunn wrote:
> Hi Nikolay
> 
> The man page says that the bridge forward_delay is in units of
> seconds, and should be between 2 and 30.
> 
> I've tested on a couple of different kernel versions, and this appears
> to be not working correctly:
> 
> ip link set br0 type bridge forward_delay 2
> RTNETLINK answers: Numerical result out of range
> 
> ip link set br0 type bridge forward_delay 199
> RTNETLINK answers: Numerical result out of range
> 
> ip link set br0 type bridge forward_delay 200
> # 
> 
> ip link set br0 type bridge forward_delay 3000
> #
> 
> ip link set br0 type bridge forward_delay 3001
> RTNETLINK answers: Numerical result out of range
> 
> I've not checked what delay is actually being used here, but clearly
> something is mixed up.
> 
> grep HZ .config 
> CONFIG_HZ_PERIODIC=y
> # CONFIG_NO_HZ_IDLE is not set
> # CONFIG_NO_HZ_FULL is not set
> # CONFIG_NO_HZ is not set
> CONFIG_HZ_FIXED=0
> CONFIG_HZ_100=y
> # CONFIG_HZ_200 is not set
> # CONFIG_HZ_250 is not set
> # CONFIG_HZ_300 is not set
> # CONFIG_HZ_500 is not set
> # CONFIG_HZ_1000 is not set
> CONFIG_HZ=100
> 
> Thanks
> 	Andrew
> 

Hi Andrew,
The man page is wrong, these have been in USER_HZ scaled clock_t format from the beginning.
TBH a lot of the time/delay bridge config options are messed up like that.
We've been discussing adding special _ms versions in iproute2 to make them
more user-friendly and understandable. Will cook a patch for the man page.

Cheers,
 Nik