Re: [PATCH 1/3] mac80211: move mesh sync beacon handler into neighbour_update

[Marco Porsch <marco@cozybit.com>]

Hi,

On 02/15/2013 02:58 PM, Johannes Berg wrote:
> On Fri, 2013-02-15 at 14:48 +0100, Marco Porsch wrote:
>
>>> I'm talking about this API:
>>>
>>> mesh_neighbour_update:
>>> ...
>>> 	tsf = drv_get_tsf()
>>> ...
>>> 	sync_ops->rx_bcn(..., tsf)
>>>
>>>
>>> mesh_sync_offset_rx_bcn(..., t_r):
>>> 	...
>>> 	if (have_better_timestamp)
>>> 		t_r = get_better_timestamp()
>>>
>>>
>>> You can hardly claim that's an intuitive API.
>>
>> Hm, alright. Just saying that ieee80211_mps_sta_tbtt_update still uses
>> the unchanged TSF value. But hey :)
>
> Well, that function doesn't exist in this patch...
>
>> What would be more favourable then?
>
> I guess you can tell I'm not in a good mood today. I think any use of
> get_tsf() for operation is a complete waste of time, there's no way you
> can get the timings correct. You could be preempted, and suddenly sleep
> for a few tens or hundreds milliseconds, so none of this makes any
> sense... To properly do it you have to do calculations in relative times
> and let the device apply them.

I don't get your last sentence here. Maybe you can elaborate?

Concerning timestamp vs. TSF usage; wow - I tested it when using the 
timestamp value for TBTT scheduling. Works fine. Works even better than 
TSF as it slightly reduces the measured wakeup overhead.

Hm, I was sure the TSF as in *now* would be more appropriate than the 
TSF at receipt time... But either way, if it works better and is less 
ugly, it is a win-win =)

I'll send an updated patch with the more intuitive API.