Re: Prevent auto scan in wireless devices

[Aloisio Almeida <aloisio almeida openbossa org>]

Well, you're right about stop background scans, it seems to change the
way that NM was structured to work.

But lets suppose the use case where you have a embedded system (or a
notebook/netbook) and you're running on battery and you don't want use
wireless that time and you don't have a rf switch button. You will
loose power keeping your wireless card on scanning at each 20 seconds,
using passive scan or not.

Why don't activate a POWER SAVING mode in nm (when running on battery)
and make it decrease the power consumption by turning the wireless
card off after X seconds disconnected and only turn it on by client
request?


On Wed, Jan 14, 2009 at 2:02 PM, Dan Williams <dcbw redhat com> wrote:
> On Tue, 2009-01-13 at 23:17 +0200, Antti Kaijanmäki wrote:
>> [Aloisio, sorry for double reply, I forgot to CC the list]
>>
>> On Tue, 2009-01-13 at 17:45 -0300, Aloisio Almeida wrote:
>> > Hi all,
>> >
>> > I noticed that wireless devices are always scanning, and this is very
>> > bad to power consuption in embedded systems.
>> > I would like to create a way to prevent automatic scan and just
>> > perform it when some cliente ask for it.
>> > Is it possible to do this? I mean, does it "brake" in some way the nm structure?
>>
>> Sounds good. Actually if you look at some current embedded devices they
>> are performing wireless scan only after user has indicated he wants to
>> create a wireless connection.
>
> I tend to think this is mainly because "it's always been done this way"
> rather than for the reason that it's actually a smoother experience for
> users.  Chips used to suck enough that they actually did require more
> power to scan, but these days with passive scans, you don't even need to
> TX, and thus you don't need to increase power that much.  If this is
> really a concern, the best approach is to simply disable the device (or
> rfkill or whatever) until the user wants to use it, at which point you
> bring the device out of rfkill and let NM go wild.
>
>> > Actually, I already did this patch to 0.6.6 version, but zero lines
>> > applied in new code :) Now i would like to create the patch and submit
>> > to upstream.
>> >
>> > The basic idea is just make can_scan function (src/nm-device-wifi.c)
>> > return FALSE due to some user configurations or run flags
>> > (--no-bg-scan). In this case, "performScan" dbus method and
>> > "ScanPerformed" dbus signal must be created to allow clients to ask
>> > for a scan and to notice that the scan has been performed.
>>
>> Would those be added in org.freedesktop.NetworkManager interface or per
>> wireless device in Device.Wireless?
>
> Not going to happen...  Again, we don't just toss stuff in before
> actually *understanding* what the problem is, and then determining if
> there are better ways of solving the problem instead of these sorts of
> hacks.
>
>> > I'm attaching the 0.6.6 patch, as I said before the idea is the same.
>> >
>> > Any comments? Is it a good way to implement that?
>>
>> I would like to have also a dbus option which you can change without
>> restarting the daemon; setScanningEnabled() or something like that.
>> '--no-bg-scan' would initialize it as false on daemon startup. It could
>> be changed during system operation based on power profiles or something
>> like that. Anyway it would give more flexibility. Of course that could
>> be too close to wirelessEnabled (), though...
>
> Again, what's the use-case here?  Are there better ways of solving this
> issue that don't impact the roaming ability performance or user
> experience?
>
> Dan
>
>
>