[gentoo-user] CPU "choking" under high load

[gentoo-user] CPU "choking" under high load

[Daniel Quinn]

I don't know if this is a hardware issue or not, but I thought that maybe I'd 
configured my kernel incorrectly and that this might be a known issue someone 
here has run across in the past so here goes:

My computer is a pretty impressive AMD 64 X2 Dual Core Processor 6400+ box 
with 2GB of RAM and for the most part, I just use it to write code at work.  
However, whenever I'm doing something CPU-intensive, two things happen:

  * The load on the box goes up to 4
  * The box intermittently wobbles from running at full-speed and dropping to
    a crawl.  This is best seen while watching Flash videos online, 
    compressing/encoding video, or compiling.  Everything is fine for a few 
    minutes, then suddenly the rate of compiling/compression/playback etc. 
    drops to a crawl for about 1-3minutes, then back up to full speed.

I don't know why it's happening.  I've tried various kernel options with no 
change in behaviour.  Outside of that though, I don't know what to try.  
Suggestions welcome :-(

Re: [gentoo-user] CPU "choking" under high load

[Kyle Bader]

> I don't know if this is a hardware issue or not, but I thought that maybe I'd
> configured my kernel incorrectly

Did this behavior start after a kernel upgrade? If yes, what was the
previous kernel version and what version are you running now?

-- 

Kyle

Re: [gentoo-user] CPU "choking" under high load

[Neil Walker]

On 26/03/10 20:47, Daniel Quinn wrote:
> I don't know why it's happening.  I've tried various kernel options with no 
> change in behaviour.  Outside of that though, I don't know what to try.  
> Suggestions welcome :-(
>   

It sounds very much to me like a lack of physical memory and your
system is resorting to the swap partition. What does free report?


Be lucky,

Neil
http://www.neiljw.net/


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Re: [gentoo-user] CPU "choking" under high load

[Dale]

Daniel Quinn wrote:
> I don't know if this is a hardware issue or not, but I thought that maybe I'd
> configured my kernel incorrectly and that this might be a known issue someone
> here has run across in the past so here goes:
>
> My computer is a pretty impressive AMD 64 X2 Dual Core Processor 6400+ box
> with 2GB of RAM and for the most part, I just use it to write code at work.
> However, whenever I'm doing something CPU-intensive, two things happen:
>
>    * The load on the box goes up to 4
>    * The box intermittently wobbles from running at full-speed and dropping to
>      a crawl.  This is best seen while watching Flash videos online,
>      compressing/encoding video, or compiling.  Everything is fine for a few
>      minutes, then suddenly the rate of compiling/compression/playback etc.
>      drops to a crawl for about 1-3minutes, then back up to full speed.
>
> I don't know why it's happening.  I've tried various kernel options with no
> change in behaviour.  Outside of that though, I don't know what to try.
> Suggestions welcome :-(
>
>    

Shot in the dark here.  Could it be that something is getting hot, or 
thinks it is getting hot, and slows down processing in a effort to cool 
things down a bit?  I don't know if this is just laptops but I think 
there is a option in the kernel to do this.  I don't use it but it may 
be worth checking into.   Maybe it was turned on by default.

Dale

:-)  :-)

Re: [gentoo-user] CPU "choking" under high load

[Paul Hartman]

On Fri, Mar 26, 2010 at 3:47 PM, Daniel Quinn
<expendable.0@danielquinn.org> wrote:
> I don't know if this is a hardware issue or not, but I thought that maybe I'd
> configured my kernel incorrectly and that this might be a known issue someone
> here has run across in the past so here goes:
>
> My computer is a pretty impressive AMD 64 X2 Dual Core Processor 6400+ box
> with 2GB of RAM and for the most part, I just use it to write code at work.
> However, whenever I'm doing something CPU-intensive, two things happen:
>
>  * The load on the box goes up to 4
>  * The box intermittently wobbles from running at full-speed and dropping to
>    a crawl.  This is best seen while watching Flash videos online,
>    compressing/encoding video, or compiling.  Everything is fine for a few
>    minutes, then suddenly the rate of compiling/compression/playback etc.
>    drops to a crawl for about 1-3minutes, then back up to full speed.
>
> I don't know why it's happening.  I've tried various kernel options with no
> change in behaviour.  Outside of that though, I don't know what to try.
> Suggestions welcome :-(

My initial thoughts, it sounds like what I experienced a few kernels
ago when they introduced the new group scheduler features. In my case
I disabled "Group CPU scheduler" in kernel config and changed from
SLUB back to SLAB. Also perhaps try to change your preemption model,
timer frequency, NO_HZ mode. These things have all had noticeable
differences to me in responsiveness over the years.

If it's not a kernel issue, perhaps use "nice" to tame CPU-hungry
processes, or "ionice" if they are disk-intensive.

Be sure your Video Card is not overheating or going into low-power
mode. Nvidia cards go into a super-slow-mode when they overheat
(happened to me 3 times when the fan on the card died). When that
happened, for example my FPS in glxgears would go from thousands down
to double digits... I could see lines painting on the screen, it was
painfully slow.

Also, if your CPU has frequency scaling make sure it's not gone crazy,
cat /proc/cpuinfo to see CPU speed, or powertop might be a more
friendly way to view the P-States.

Download memtest86+ from memtest.org and run it to be sure you don't
have any faulty RAM (in my experience tests 5 and 8 are the only ones
that ever show any errors, so you can save time by only running one
full pass of all tests and then a multiple passes of 5 and 8 just to
be sure it's good)

Re: [gentoo-user] CPU "choking" under high load

[Paul Hartman]

On Fri, Mar 26, 2010 at 5:43 PM, Dale <rdalek1967@gmail.com> wrote:
> Daniel Quinn wrote:
>>
>> I don't know if this is a hardware issue or not, but I thought that maybe
>> I'd
>> configured my kernel incorrectly and that this might be a known issue
>> someone
>> here has run across in the past so here goes:
>>
>> My computer is a pretty impressive AMD 64 X2 Dual Core Processor 6400+ box
>> with 2GB of RAM and for the most part, I just use it to write code at
>> work.
>> However, whenever I'm doing something CPU-intensive, two things happen:
>>
>>   * The load on the box goes up to 4
>>   * The box intermittently wobbles from running at full-speed and dropping
>> to
>>     a crawl.  This is best seen while watching Flash videos online,
>>     compressing/encoding video, or compiling.  Everything is fine for a
>> few
>>     minutes, then suddenly the rate of compiling/compression/playback etc.
>>     drops to a crawl for about 1-3minutes, then back up to full speed.
>>
>> I don't know why it's happening.  I've tried various kernel options with
>> no
>> change in behaviour.  Outside of that though, I don't know what to try.
>> Suggestions welcome :-(
>>
>>
>
> Shot in the dark here.  Could it be that something is getting hot, or thinks
> it is getting hot, and slows down processing in a effort to cool things down
> a bit?  I don't know if this is just laptops but I think there is a option
> in the kernel to do this.  I don't use it but it may be worth checking into.
>   Maybe it was turned on by default.

Sometimes in the BIOS this happens, too. At work a few years ago we
had a Dell laptop where it thought the temperature was 200C degrees
all the time, so it would run the fan at full speed and go into
lowest-power mode etc. Once we determined it wasn't really 200C, we
found out it was a buggy BIOS and upgrading it solved the problem.
Nobody knows why the laptop worked fine for 2 years and then suddenly
exhibited this problem, but I was glad to get it fixed so I would stop
hearing the fan blowing at max speed in the cubicle next to mine. :)

Re: [gentoo-user] CPU "choking" under high load

[Johannes Kimmel]

Paul Hartman wrote:
> On Fri, Mar 26, 2010 at 5:43 PM, Dale <rdalek1967@gmail.com> wrote:
>> Daniel Quinn wrote:
>>> I don't know if this is a hardware issue or not, but I thought that maybe
>>> I'd
>>> configured my kernel incorrectly and that this might be a known issue
>>> someone
>>> here has run across in the past so here goes:
>>>
>>> My computer is a pretty impressive AMD 64 X2 Dual Core Processor 6400+ box
>>> with 2GB of RAM and for the most part, I just use it to write code at
>>> work.
>>> However, whenever I'm doing something CPU-intensive, two things happen:
>>>
>>>   * The load on the box goes up to 4
>>>   * The box intermittently wobbles from running at full-speed and dropping
>>> to
>>>     a crawl.  This is best seen while watching Flash videos online,
>>>     compressing/encoding video, or compiling.  Everything is fine for a
>>> few
>>>     minutes, then suddenly the rate of compiling/compression/playback etc.
>>>     drops to a crawl for about 1-3minutes, then back up to full speed.
>>>
>>> I don't know why it's happening.  I've tried various kernel options with
>>> no
>>> change in behaviour.  Outside of that though, I don't know what to try.
>>> Suggestions welcome :-(
>>>
>>>
>> Shot in the dark here.  Could it be that something is getting hot, or thinks
>> it is getting hot, and slows down processing in a effort to cool things down
>> a bit?  I don't know if this is just laptops but I think there is a option
>> in the kernel to do this.  I don't use it but it may be worth checking into.
>>   Maybe it was turned on by default.
> 
> Sometimes in the BIOS this happens, too. At work a few years ago we
> had a Dell laptop where it thought the temperature was 200C degrees
> all the time, so it would run the fan at full speed and go into
> lowest-power mode etc. Once we determined it wasn't really 200C, we
> found out it was a buggy BIOS and upgrading it solved the problem.
> Nobody knows why the laptop worked fine for 2 years and then suddenly
> exhibited this problem, but I was glad to get it fixed so I would stop
> hearing the fan blowing at max speed in the cubicle next to mine. :)
> 

I have the very same problem with my GX700 msi laptop. I determined the 
   cause was a dirty cooler. Every time I blow the dust out of the fan 
it can run hours without throttling itself.

If maybe your cpu-cooler is undersized and has collected a lot of dust, 
cleaning it could solve your problem.

Johannes