

Linux Power Usage Regression in 2.6.38+ - tagx
http://www.phoronix.com/scan.php?page=news_item&px=OTM2NQ

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jerf
It isn't just me then, huh? I tried to bisect my way to a precise patch but
it's really hard when you have ~15 steps, it's hard to tell if it "works" or
not in anything less than an hour, and if you're wrong once you're guaranteed
not to find the correct one. And the results I got almost make me think it's
actually more than one patch combining together such that it has actually
gotten gradually worse over time, which makes it even harder to finger.

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vimes656
As Linus already acknowledged the kernel is getting dangerously bloated.

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rbanffy
I think it's time to have some unit tests written and get bolder with
refactoring. I remember smarter-than-me developers claiming it's impossible to
have tests in the kernel, but I never quite got a satisfactory answer. BTW, is
there a USB connected power meter that could be used to reliably measure power
consumption? It's easy to setup abox that continuously deploys different
kernel configurations and measures power consumption. With something like that
we could have a good map of power consumption x kernel x hardware in a couple
days.

~~~
eli
Perhaps you could actually see a difference in current with a Kill-A-Watt or
similar.

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rbanffy
But that would be a manual step. The idea behind this would be to let the box
build and test a succession of kernels, patch by patch, automatically, to find
a regression.

I wouldn't want to manually test a hundred kernels, but I can easily spare a
box for a week.

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eli
Ah, now I'm with you. I believe the high-end model does indeed have a USB
connection though I would expect the software to be terrible

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rbanffy
All we would need would be some way to gauge the instantaneous consumption at
reading time. I would assume the tested kernel is capable of, at least, boot,
check its power consumption under some workload (maybe compiling the kernel
with the next patch set to be tested) and dumping that information to a file
or a remote machine.

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lloeki
I installed/upgraded ArchLinux (which is at 2.6.38 now) on a bunch of laptops
lately and noticed a raise in power usage (in the range of 10%), with mostly
some high kworker activity (100+ wakeup/s when idle, that's 80% of overall
wakeups) in powertop. But the worst contender has been s2ram power usage: the
laptops go to sleep yet leaving them sleeping overnight pumps 40% out of the
battery (should be 2~4%, tops). Unfortunately I can't downgrade easily as .38
introduced proper support for core components of those laptops.

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moondowner
.38 introduced lot's of new stuff [1], so regressions can occur I guess. But I
know that it'll get fixed. By the time this news got to HN there's probably
someone working on it.

[1] <http://kernelnewbies.org/Linux_2_6_38>

~~~
jedbrown
Transparent huge pages (also new in 2.6.38) have caused about 5% degradation
in memory bandwidth (measured by STREAM benchmarks and other kernels,
independent of the use of software prefetch) on my machines. This is somewhat
strange because huge pages should help this benchmark.

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tagx
It will be interesting to see how this plays out when Ubuntu 11.04 which uses
2.6.38 is released.

