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Power impact of debufferbloatingPower impact of debufferbloatingPosted Sep 13, 2011 19:27 UTC (Tue) by Richard_J_Neill (subscriber, #23093)In reply to: Power impact of debufferbloating by arjan Parent article: LPC: An update on bufferbloat
Really? On my Android phone, the CPU is about the least power-hungry part. By a huge margin, the power-hog is the screen's backlight.
BTW, have you ever noticed that web-access on a 3G phone is sometimes really, really, really slow (20 seconds + for a google query, yet simultaneously quite quick for a large webpage load)? This is buffer bloat in action.
Lastly, it's worth pointing out that the Application can still buffer all it wants; we are considering the TCP buffering here. If my application wants to send a 1 MB file, there is no reason why the kernel shouldn't give userspace a whole 1MB of zero-copy buffer. That's outside the TCP end-points. The problem is that the TCP-end-points themselves need to see timely packet loss, in order to back-off slightly on transmit rates.
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Power impact of debufferbloating Posted Sep 13, 2011 19:35 UTC (Tue) by arjan (subscriber, #36785) [Link]
I think you're mistaken in thinking such activity bursts only impact the CPU.
Memory is equally impacted (going between fully active and self refresh), as are other parts of the chipset. And cpu + memory + chipset do make up a significant part of system power. Sure the screen takes a lot too.. but to get reasonable power you need to look across everything that's significant.
Power impact of debufferbloating Posted Sep 14, 2011 6:07 UTC (Wed) by ringerc (subscriber, #3071) [Link]
That *can* be buffer bloat in action. It's just as often to do with the mostly-transparent base station roaming your phone does, its radio power management, the base station's load, the insane complexity of the HSPA+/HSPA/HSDPA/UMTS/GSM stack(s), the endless layers of weird and varied legacy crap that live under them, etc.
My phone will often poke away for a while trying to use a data connection, conclude it's not working, re-establish it, conclude it's still not working, switch to 2G (GPRS) and set that up, roam to a new base station as signal strenth varies, try to upgrade to 3G again, fail, and then eventually actually do what I asked.
Realistically, unless you're trying to do a google search while numerous other nearby people are watching TV / streaming video / downloading files / etc on their phones on the same network, it's probably more likely to be regular cellular quirks than bufferbloat.
As for power: Yep, the screen gets the blame for the majority of the power use on android phones. I can't help suspecting that means "display and GPU" though, simply because of the overwhelming power use. That's a total guess, but if GPU power is attributed under "System" then (a) it's insanely efficient and (b) Apple have invented new kinds of scary magic for their displays to allow them to run brighter, better displays for longer on similar batteries to Android phones.
Power impact of debufferbloating Posted Sep 14, 2011 7:05 UTC (Wed) by Los__D (guest, #15263) [Link]
Erm, The only thing that Apple has on Andorid phones is resolution. I.e. the Galaxy S2's Super AMOLED Plus (damn I hate that name) has a brighter screen with deeper colors.
Power impact of debufferbloating Posted Sep 14, 2011 14:48 UTC (Wed) by Aissen (subscriber, #59976) [Link]
Infinite contrast and vibrant colors, yes. Bright, I wouldn't say that:
http://www.anandtech.com/show/4686/samsung-galaxy-s-2-int...
(I'm one of those who went the AMOLED route and will probably never come backĀ
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Power impact of debufferbloating Posted Sep 14, 2011 17:04 UTC (Wed) by Los__D (guest, #15263) [Link]
That is a strange chart, besides own my comparisons (both devices @100%), there are several comparisons on YouTube, also showing a much brighter screen on the S2:
http://www.youtube.com/watch?v=_BXWqkOexiU&feature=fv... http://www.youtube.com/watch?v=UyalqkdVk-8 (this is a bit flawed, as it is from quite an angle).
OTOH, I've seen many complaints about low brightness and yellowish tint on the S2, maybe there are different versions of the screen?
Power impact of debufferbloating Posted Sep 14, 2011 8:19 UTC (Wed) by lab (subscriber, #51153) [Link]
>Really? On my Android phone, the CPU is about the least power-hungry part. By a huge margin, the power-hog is the screen's backlight.
Yes exactly. This is a wellknown fact. If you have an AMOLED (variant) screen, everything light/white consumes a lot of power. Black nothing.
>BTW, have you ever noticed that web-access on a 3G phone is sometimes really, really, really slow (20 seconds + for a google query, yet simultaneously quite quick for a large webpage load)? This is buffer bloat in action.
Interesting. I have the same observation, and always thought of it as "the mobile web has huge latency but quite good bandwidth".
Power impact of debufferbloating Posted Sep 15, 2011 6:44 UTC (Thu) by Cato (subscriber, #7643) [Link]
Your anecdote about web page load times could equally be due to changed cell usage by other phones, or by congestion on the backhaul link from the cellsite to the mobile networks IP aggregation/core network. Without repeated measurements it's not really possible to say what's causing a delay.
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