On Wed, 2009-03-25 at 21:53 +0200, Kalle Valo wrote:
> > By the way, do you have any numbers on how the timeout affects actual
> > network latency?
>
> Nope. I would guess that there are academic studies about this and if
> someone finds anything, please share them here. I would interested as
> well.
Too bad :) I guess we could go measure some...
> > It's also related to the beacon interval and the listen interval, of
> > course.
>
> Yes. Also we need to consider are we willing to skip DTIM beacons and
> loose multicast/broadcast frames. We could save even more power with
> that.
Right -- iwlwifi seems to do that sometimes.
> > I'm just worried that we'll require a whole bunch of different
> > interfaces. Yes, in theory there isn't much to control, but iwlwifi
> > firmware for example can, as far as I interpret the code, dynamically
> > vary the listen interval.
>
> You mean the wakeup interval? For me, listen interval means the
> maximum time AP is willing to buffer frames for a STA.
No, I mean the listen interval in the assoc request frame.
> I assume you mean sleep_interval here:
>
> #define IWL_POWER_VEC_SIZE 5
>
> struct iwl_powertable_cmd {
> __le16 flags;
> u8 keep_alive_seconds; /* 3945 reserved */
> u8 debug_flags; /* 3945 reserved */
> __le32 rx_data_timeout;
> __le32 tx_data_timeout;
> __le32 sleep_interval[IWL_POWER_VEC_SIZE];
> __le32 keep_alive_beacons;
> } __attribute__ ((packed));
>
> So there's an array sleep/wakeup interval, which firmware most
> probably rotates periodically.
I don't actually know what the sleep interval here is...
> I think stlc45xx/p54 even had something
> similar. But honestly, I don't know if this kind of trickery is
> useful. Why not directly go to the longest wakeup interval
> immediately?
But listen interval * beacon interval determines latency.
> My view is that the decision to change wakeup interval should be done
> in host, preferably userspace. Userspace has the best knowledge, it
> should make the decision as well.
What's the wakeup interval?
> > Some of the decisions might also depend on the hardware, I could
> > imagine, the point where turning off power saving is required might be
> > different depending on hardware due to wakeup time maybe?
>
> Yes, there might be some differences.
How would we capture these?
johannes
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