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DirtyHairy
l33t
Joined: 03 Jul 2006
Posts: 608
Location: Würzburg, Deutschland
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 Posted: Mon Aug 15, 2011 8:48 pm Post subject: Power consumption regression for sandy bridge in 3.0 |
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The following problem has cost me a couple of hours, and I thought that I might create a short post in order to save others the trouble  Updating my laptop (core i7 / HD 3000 IGP) from 3.0-rc7 vanilla to gentoo-sources-3.0.1 caused a serious increase in power consumption of about 3-5 watts. After a bit of research, it turns out that a broken-by-design type power management regression was introduced into the i915 driver somewhere between rc7 and 3.0 final: a deep sleep (from what I gather) state of the GPU was disabled by default as it seems to cause issues for some people. The issue is discussed on https://bugs.launchpad.net/ubuntu/+source/linux/+bug/818830 ; in short, adding the boot option | Code: | | i915.i915_enable_rc6=1 |
reenables this features and restores the previous behavior. Hope this helps someone  |
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morpheus2051
Tux's lil' helper
Joined: 07 May 2006
Posts: 95
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| Posted: Mon Aug 15, 2011 10:42 pm Post subject: |
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Thanks for pointing this out. My laptop runs cooler than before. I did not test the runtime on battery yet. Hope this brings battery life back up again. Since kernel 3.0 is the first kernel with which I do not have any system-hard-locks. But my runtime on battery is not near as good as it is with windows7. On windows7 my system actually runs about one and a half hour longer than under linux.
Do you have this parameter enabled?
It helped me a little bit. |
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DirtyHairy
l33t
Joined: 03 Jul 2006
Posts: 608
Location: Würzburg, Deutschland
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| Posted: Tue Aug 16, 2011 9:01 am Post subject: |
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| morpheus2051 wrote: | | Since kernel 3.0 is the first kernel with which I do not have any system-hard-locks. |
Same with me, I was getting occasional system freezes with 2.9.39 which is why I switched to the 3.0 release candidates in the first place.
| morpheus2051 wrote: |
But my runtime on battery is not near as good as it is with windows7. On windows7 my system actually runs about one and a half hour longer than under linux. |
As I use linux fulltime, I was to lazy to do a direct comparison. However, my machine lasts around 5 hours on linux, which is enough for my purposes.
| morpheus2051 wrote: |
Do you have this parameter enabled?
It helped me a little bit. |
I tried it when I read about it, but it didn't affect me in any way. |
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albright
Advocate
Joined: 16 Nov 2003
Posts: 2588
Location: Near Toronto
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| Posted: Tue Aug 16, 2011 12:49 pm Post subject: |
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| Quote: | in short, adding the boot option
| Code: | | i915.i915_enable_rc6=1 |
reenables this features and restores the previous behavior. Hope this helps someone |
thanks for that - according to powertop, enabling that option drops my
power consumption by more than a watt (which is quite a lot on my
thinkpad x300, it now - with wireless of and screen half-bright - uses
about 7.5 watts; a couple of watts more with wireless on - I **DO**
wish the iwl4965 driver had powersaving ...)
_________________
.... there is nothing - absolutely nothing - half so much worth
doing as simply messing about with Linux ...
(apologies to Kenneth Graeme) |
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