[Buildroot] [PATCH] busybox: register mdev as hotplug helper

Thomas De Schampheleire patrickdepinguin+buildroot at gmail.com
Sun Jul 28 08:33:24 UTC 2013


Hi,

On Fri, Jul 12, 2013 at 12:27 PM, Gustavo Zacarias
<gustavo at zacarias.com.ar> wrote:
> On 07/12/2013 04:01 AM, Thomas De Schampheleire wrote:
>> In linux/linux.mk, there mdev is already set as hotplug helper in the
>> kernel configuration.
>> How does this change relate to it? At first sight, it seems unnecessary.
>>
>> I did notice that setting mdev as hotplug helper in the kernel
>> configuration, can seriously impact boot performance. On a board with
>> a not so fast single core processor (around 500MHz) boot time until
>> userspace became about 10 seconds coming from 2s. We solved this by
>> setting no helper in the kernel configuration (and telling buildroot
>> to use just devtmpfs instead of mdev), and manually copying S10mdev to
>> the rootfs. Then, mdev is run once during userspace init.
>> This doesn't give automatic firmware loading, but that would be solved
>> by your above patch, I think.
>>
>> Did anyone else notice such slowdown behavior?
>
> I actually came up with this patch because a user on a pandaboard had
> issues getting the wifi up (wl127x, needs firmware).
> At first he was running a static device tree configuration which
> explained the problem.
> He then switched to mdev and things didn't work, and switching to udev
> did make it work.
> So i looked at S10mdev and saw that the hotplug helper wasn't registered.
> It's likely that he didn't make clean between switching to mdev and the
> kernel hence didn't get reconfigured/rebuilt and that was the problem.
> However as you say, if the kernel has pre-registered the hotplug helper
> in the configuration all the hotplug events at boot time are probably
> getting called (all the bus interfaces and whatnot).
> I tend to use my own initscripts tree since it's quite tweaked regarding
> the bare default (i basically nuke all of buildroots initscripts and
> replace them with my own), and on an arm920t (slow really, 180 mhz) i
> have no major delay when using this method.
> The only "drawback" would be missing usb devices if they're already
> plugged in and the usb controller driver isn't a module - but really
> that's coldplug-world.
> Regards.
>

So what do we do with this patch?
I ask it because it's still marked as 'New' in patchwork:
http://patchwork.ozlabs.org/patch/258619/
If we agree that it shouldn't be needed, I suggest to mark it as such.
If someone can come up with a proven failure scenario, we can still reopen it.

What do you think?

Thanks,
Thomas


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