Message-ID: <1361200801.8555.29.camel@jlt4.sipsolutions.net> (sfid-20130218_162014_601375_F4347BE7)
Subject: Re: [PATCH 1/3] mac80211: move mesh sync beacon handler into
 neighbour_update
From: Johannes Berg <johannes@sipsolutions.net>
To: Marco Porsch <marco@cozybit.com>
Cc: mcgrof@qca.qualcomm.com, jouni@qca.qualcomm.com,
	vthiagar@qca.qualcomm.com, senthilb@qca.qualcomm.com,
	linux-wireless@vger.kernel.org, devel@lists.open80211s.org,
	ath9k-devel@lists.ath9k.org
Date: Mon, 18 Feb 2013 16:20:01 +0100
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References: <1360928446-543-1-git-send-email-marco@cozybit.com>
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On Mon, 2013-02-18 at 16:07 +0100, Marco Porsch wrote:

> > 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?

I'm saying what could happens is this:

 tsf = drv_get_tsf()
 [be preempted, 100ms later]
 do_something_with(tsf)

so I think using drv_get_tsf() is pretty much always wrong.


> 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.

:)

johannes