Re: cpu0/online No such file or directory

On 07/26/2018 03:39 PM, Justin Michael Schwartzbeck wrote:
> Hello,
> 
> I have compiled oprofile 1.3.0 for wind river linux and have attempted to do a basic test on the installed system:
> 
> # x86_64-wrs-linux-operf ls
> 
> However I get the following error:
> 
> Unable to open /sys/devices/system/cpu/cpu0/online
> No such file or directory
> Unable to open /sys/devices/system/cpu/cpu0/online
> No such file or directory
> Caught runtime_error: Internal Error: Number of online cpus cannot be determined.
> Error running profiler
> 
> I confirmed that I am indeed missing /sys/devices/system/cpu/cpu0/online. I have found that this file is present for cpu1, cpu2, etc. but not for cpu0. I have googled this a lot and most people seem to say that this is because cpu0 cannot go offline, so the file is nonexistent.
> 
> Can someone help me get around this issue?
> 
> Thanks
> -Justin

Hi Justin,

It does seem odd that the /sys/devices/system/cpu/cpu0 directory is missing, but all the others are there. Given that this looks like an issue with the kernel it would be helpftul to provide a bit more information about the kernel.  What version of the kernel is being used.  Are there any unusual configurations or patchs in the kernel.  I know that some MIPS configurations can split a processor off to handle some embedded control and the linux kernel does not manage it (sorrty I don't have a handy link for this).  Is this x86 machine doing something similar?  Take a look through the output of dmesg to see what it is doing to start up the processors.

-Will




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