Re: [PATCHv2 6/6] mac80211: mesh power save basics

[Marco Porsch <marco@cozybit.com>]

On 01/16/2013 11:14 PM, Johannes Berg wrote:
> On Mon, 2013-01-07 at 16:04 +0100, Marco Porsch wrote:
>
>> mode determines when non-peer mesh STA may send Probe Requests and Mesh Peering
>
> Please break lines to less than 72 characters, I personally prefer
> around 60 or so but I'll apply 72 too.
>
>> +static inline bool ieee80211_has_qos_mesh_ps(__le16 qc)
>> +{
>> +	return (qc & cpu_to_le16(IEEE80211_QOS_CTL_MESH_PS_LEVEL)) != 0;
>
> bool means you don't need the !=0 and parentheses.
>
>
>> @@ -1208,6 +1214,7 @@ struct ieee802_11_elems {
>>   	struct ieee80211_meshconf_ie *mesh_config;
>>   	u8 *mesh_id;
>>   	u8 *peering;
>> +	u8 *awake_window;
>
> maybe that should be an __le16 pointer?
>
>> +			/* we need some delay here, otherwise the announcement
>> +			 * Null would arrive before the CONFIRM
>> +			 */
>> +			ieee80211_mps_set_sta_local_pm(sta, mshcfg->power_mode,
>> +						       100);
>
> ???
>
> How can a *delay* ever cause correctness? That doesn't seem right.

That was needed because a QoS Null used to inform the peer was often 
received before the Peer Link Confirm frame and thus thrown away. 
Luckily, after testing that once again, the problem has magically 
vanished. I'll remove the whole timer thing--never liked having that 
anyway.

>> +	/* announce peer-specific power mode transition
>> +	 * see IEEE802.11-2012 13.14.3.2 and 13.14.3.3
>> +	 */
>
> I feel a bit bad about asking this, but mac80211 actually doesn't use
> the "networking" style, all other comments have
>
>   /*
>    * announce ...
>    * ...
>    */
>
> so please adjust yours as well.

Oops. checkpatch fooled me here.

> I think I deleted this, but nonetheless:
>
>
>> static void mpsp_trigger_send(struct sta_info *sta,
>>                                bool rspi, bool eosp)
>
> that easily fits on one line.
>
>
>> +/**
>> + * mps_frame_deliver - transmit frames during mesh powersave
>> + *
>> + * @sta: STA info to transmit to
>> + * @n_frames: number of frames to transmit. -1 for all
>> + */
>> +static void mps_frame_deliver(struct sta_info *sta, int n_frames)
>> +{
>> +	struct ieee80211_sub_if_data *sdata = sta->sdata;
>> +	struct ieee80211_local *local = sdata->local;
>> +	int ac;
>> +	struct sk_buff_head frames;
>> +	struct sk_buff *skb;
>> +	bool more_data = false;
>> +
>> +	skb_queue_head_init(&frames);
>
> You really don't need a spinlock for on-stack queues, so you should use
> the __ versions of the functions modifying "frames".

Yeah, right. The skb_queue_head_init needs to stay, though, because of 
ieee80211_add_pending_skbs_fn.

>
>> +			if (!skb)
>> +				break;
>> +			n_frames--;
>
> I guess you're assuming there never will be > 2^31 frames ;-)

In that case something else would crash first, I hope =)
Btw, that code is very similar to ieee80211_sta_ps_deliver_response.

>> +			skb_queue_tail(&frames, skb);
>
> __skb_queue_tail(), etc.
>
>> +		}
>> +
>> +		if (!skb_queue_empty(&sta->tx_filtered[ac]) ||
>> +		    !skb_queue_empty(&sta->ps_tx_buf[ac])) {
>> +			more_data = true;
>> +		}
>
> No need for the braces
>
>> +	/* in a MPSP make sure the last skb is a QoS Data frame */
>> +	if (test_sta_flag(sta, WLAN_STA_MPSP_OWNER))
>> +		mpsp_qos_null_append(sta, &frames);
>
>
>
>> +	mps_dbg(sta->sdata, "sending %d frames to PS STA %pM\n",
>> +		skb_queue_len(&frames), sta->sta.addr);
>> +
>> +	/* prepare collected frames for transmission */
>> +	skb_queue_walk(&frames, skb) {
>> +		struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
>> +		struct ieee80211_hdr *hdr = (void *) skb->data;
>> +
>> +		/* Tell TX path to send this frame even though the
>> +		 * STA may still remain is PS mode after this frame
>> +		 * exchange.
>> +		 */
>> +		info->flags |= IEEE80211_TX_CTL_NO_PS_BUFFER;
>
> I'm not convinced that the PS integration with drivers here is correct
> at all, but I don't really care all that much either.

That flag is picked up by the mac80211 TX handlers to bypass the TX 
buffer. We currently do not support any driver/HW that buffers frames 
itself; even aggregation is causing trouble already.

>> + * @WLAN_STA_MPSP_OWNER: local STA is owner of a mesh Peer Service Period.
>> + * @WLAN_STA_MPSP_RECIPIENT: local STA is recipient of a MPSP.
>> + * @WLAN_STA_MPS_WAIT_FOR_BEACON: STA beacon is imminent -> stay awake
>> + * @WLAN_STA_MPS_WAIT_FOR_CAB: STA multicast frames are imminent -> stay awake
>
> ??

Oops, that belongs into a following commit on device sleep for actual 
power savings that I am currently testing.

> There's also a compiler warning -- variable shadowing -- that this
> probably solves:
>
> @@ -487,8 +487,6 @@ static void mps_frame_deliver(struct sta_info *sta,
> int n_frames)
>
>          /* collect frame(s) from buffers */
>          for (ac = 0; ac < IEEE80211_NUM_ACS; ac++) {
> -               struct sk_buff *skb;
> -
>                  while (n_frames != 0) {
>                          skb = skb_dequeue(&sta->tx_filtered[ac]);
>                          if (!skb) {
>
>
> johannes
>