Timo Sirainen wrote:
On Tue, 2009-10-13 at 21:38 +0100, Ed W wrote:
Something I had been pondering recently (I started using a cell phone
with imap idle support), was a previous poster mentioning the huge
increase in battery life from turning off the radio for as long as
possible. It appears that just turning on the radio (wifi or 3G)
consumes much more energy than the transmitting of a few bytes of data
after it's on. In particular synchronising certain types of infrequent
transmissions may have a dramatic increase in battery life for mobile
devices - I'm thinking mainly of the NOOPs when the connection is idling
Is this something that could be implemented with the current
architecture? Are there other types of application where synchronising
"stuff" happening to multiple connections from the same client could be
helpful?
No matter how many times I read the above, I've no idea what you're
trying to ask. :) This seems like entirely a client-dependent issue and
Dovecot can't much alter clients' behavior. Unless you're talking about
running Dovecot on a cell phone?..
Perhaps I misunderstand, but doesn't dovecot send a "keepalive" on
connections which are idling? It's been discussed on the list
previously, google turns up this (not from the list, but related):
http://doubleukay.com/node/12
I hadn't previously twigged for example that the real reason using my
old Nokia N95 as a wifi SIP phone was caning the battery could have been
the short re-registration interval as much as actually having the phone
on wifi. I now have an N97 and the buggers disabled the SIP phone bit,
but there is some hope it will be re-enabled on the next firmware update
- I was planning to do a bit of research on this if so.
The point being that for wireless users there is a massive "cost" to
turn on the radio and transmit any data, the actual transmission of
incremental data after that is cheap. So applications and servers which
may operate over wireless networks can massively increase battery life
if they give some thought to significantly "batching up" network traffic
I can imagine that in the case of a typical cell phone with say 3 email
accounts, there will be likely three idle connections (or more) to
dovecot and each will end up sending keepalive packets at slightly
different intervals for each connection. By synchronising this network
traffic you would potentially increase battery life by up to a factor of
3 (ie turn on the radio to send the keepalive for all connections in one
go, rather than turning the radio on three times as often)... (I think
perhaps that's optimistic, but you can see that quite large gains might
be possible here)
Nokia make a rather neat battery optimisation tool which allows you to
log power consumed very precisely (and hopefully to correlate it to what
your app is doing) - I would like to find the time to break this out to
have a closer peak at some of this stuff, but it remains on my todo list
right now...
Cheers
Ed W
