Re: [PATCH v9] mac80211: Optimize scans on current operating channel.

[Ben Greear <greearb@candelatech.com>]

On 02/02/2011 10:55 AM, Johannes Berg wrote:
> On Wed, 2011-02-02 at 10:18 -0800, greearb@candelatech.com wrote:
>
>> * Do no blindly go off/on channel in work.c  Instead, only call
>>    appropriate on/off code when we really need to change channels.
>
> Based on the powersave comments I had earlier, maybe we should remove
> that bit for now? Work items here require powersave is disabled, but we
> won't do that right now if we're on the same channel.

The problem is, if we leave the work_work() in the original
manner, the on/off channel state changes are not properly
tracked because work blindly assumes it goes off/on channel.
This breaks assumptions about when we must call the return-to-channel
logic.  I think if we do not religiously track the on/off channel
state changes it would be too easy to get in a state where we think
we are on-channel but haven't actually re-enabled xmit queues, etc.

I think I would rather change the work logic to expressly disable/enable
powersave.  That wouldn't be difficult, would it?

> Scan, on the other hand, will still disable powersave (right?)

I don't think it does anything if we are scanning on-channel
with my patch.
The enable/disable logic is now in the offchannel code...

Do we need to disable it if we are scanning on channel?  If so,
I can add that explicitly to the scanning code.


While we are on that topic, it seems the conf.flags are set
opposite to what I expect.  Is that code below correct?

/* inform AP that we are awake again, unless power save is enabled */
static void ieee80211_offchannel_ps_disable(struct ieee80211_sub_if_data *sdata)
{
	struct ieee80211_local *local = sdata->local;

	if (!local->ps_sdata)
		ieee80211_send_nullfunc(local, sdata, 0);
	else if (local->offchannel_ps_enabled) {
		/*
		 * In !IEEE80211_HW_PS_NULLFUNC_STACK case the hardware
		 * will send a nullfunc frame with the powersave bit set
		 * even though the AP already knows that we are sleeping.
		 * This could be avoided by sending a null frame with power
		 * save bit disabled before enabling the power save, but
		 * this doesn't gain anything.
		 *
		 * When IEEE80211_HW_PS_NULLFUNC_STACK is enabled, no need
		 * to send a nullfunc frame because AP already knows that
		 * we are sleeping, let's just enable power save mode in
		 * hardware.
		 */
		local->hw.conf.flags |= IEEE80211_CONF_PS;

Thanks,
Ben

>
> johannes


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com