Re: [PATCH v3] printk: add option to print cpu id

On Fri, Aug 3, 2012 at 3:13 PM, Greg KH [off-list ref] wrote:

On Fri, Aug 03, 2012 at 03:07:39PM -0700, Pandita, Vikram wrote:

quoted

On Fri, Aug 3, 2012 at 2:59 PM, Greg KH [off-list ref] wrote:

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On Fri, Aug 03, 2012 at 02:24:20PM -0700, Pandita, Vikram wrote:

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Aaro

On Fri, Aug 3, 2012 at 1:08 PM, Aaro Koskinen [off-list ref] wrote:

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Hi,

On Fri, Aug 03, 2012 at 11:25:37AM -0700, Pandita, Vikram wrote:

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And really: Wasting 1/3 of the 80 character line is too much.

You _WASTE_ 4 chars only if you are interested in this info by
enabling: CONFIG_PRINTK_CPUID

I guess you waste 4 + 3 chars? You could optimize the length by checking
CONFIG_NR_CPUS?

Good point.
Looks there is a variable 'nr_cpu_ids' that could be used as well.

If there is general consensus that the patch can help the arm
community, and others in general,
this optimization should be easy to implement - saving few chars space
in each line of console output.

For now i will stick to this v3 version of path, unless you think otherwise.

I don't think is is something that anyone needs, and if you do, as
pointed out, you can use the trace function to make it happen.

This was something that got used internally and helped at times.

Could you have used the trace point instead?

As i understood the trace_prink(), one would need to modify existing
printk -> trace_printk. Is my understanding correct?

Most of the times the problem exhibits as a random hang, without having a clue
which code to modify. That time one generic defconfig global switch is
your first tool.

Other issue i found, using this patch, that on multi-core ARM systems,
almost 99% of times, IRQ's are handled by CPU0,
even if CPU0 was really busy and other CPU's were free. I am yet to
understand a good reason why.

this patch also helped in other areas as mentioned in the thread
http://marc.info/?l=linux-omap&m=134401269106619&w=2

Not sure how easy its to use trace_printk for such issues, i found
having one defconfig option was much easier
to get going. Correct me if i have not understood trace_printk well enough.

greg k-h