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Odward
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Joined: 21 Mar 2012
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PostPosted: Wed Apr 09, 2014 7:38 am    Post subject: gentoo-sources-3.12.13 and ksoftirqd cpu usage Reply with quote

After upgrading from gentoo-sources-3.10.25 to 3.12.13 I noticed my CPU temp was up and my activity monitor widget indicated CPU usage when it should have been idle.
Using top I see that ksoftirqd/X has 1 or 2 cores, varies from 1 boot to the next, pegged 98-100% non stop. I can reboot with kernel 3.10.25 and the problem disappears.
I don't have any idea how to begin diagnosing interrupt problems.

Checking cat /proc/interrupts after 1 boot into each kernel, to the console. Both examples are approx 5 minutes uptime. Edited for space to show offending interrupt.
Kernel-3.10.25
Code:
            CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7
 LOC:        570        871       2725        975       1497        929        751        771   Local timer interrupts

Kernel-3.12.13 (Only ksoftirqd/2 on this boot, frequently will be a second i.e. ksoftirqd/0)
Code:
            CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7
 LOC:        853       3423      60663        818        877        614         36        953   Local timer interrupts


There were also more differences with the resulting .config after compiling the new kernel, but just randomly checking for IRQ in the diff I see kernel 3.10.25 contains
Code:
< CONFIG_HAVE_GENERIC_HARDIRQS=y
< CONFIG_GENERIC_HARDIRQS=y

Those do not exist for 3.12.13 and if I read correctly those are set by X86=y and both kernel .configs contain
Code:
CONFIG_X86=y


Curious if anyone can give me a more clear nudge in the right direction. I have no problem sticking with 3.10.25 but I'm concerned if I don't figure out the right kernel config I could have this issue with any newer kernels. I suppose I could try a newer kernel =) but maybe I learn something this way too.

Thanks for your time
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Keruskerfuerst
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PostPosted: Thu Apr 10, 2014 7:06 pm    Post subject: Reply with quote

How did you configure the new kernel?
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Odward
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Joined: 21 Mar 2012
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PostPosted: Fri Apr 11, 2014 6:45 am    Post subject: Reply with quote

In a nutshell, I just copy the .config for the existing kernel. After issuing 'make menuconfig' for the new kernel I exit and am prompted to save my config. I run make && make modules_install from there. Copy to boot etc.

I've been doing that for a bit over 2 years now, since I started using Gentoo (linux for that matter). This is the same hardware on which it's been running that time too. Originally I took the time to create a kernel appropriate for my hardware, to the best of my ability, and then the above method ever since.
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