Re: get_irq_regs() from soft IRQ

[Jean Pihet <jpihet@mvista.com>]

Hi Siarhei Siamashka,
On Monday 29 June 2009 18:36:57 Siarhei Siamashka wrote:
> On Monday 29 June 2009 17:31:18 ext Jean Pihet wrote:
> > Hi,
> >
> > I am trying to get the latest IRQ registers from a timer or a work queue
> > but I am running into problems:
> > - get_irq_regs() returns NULL in some cases, so it is unsuable and even
> > causes crash when trying to get the registers values from the returned
> > ptr - I never get user space registers, only kernel
> >
> > The use case is that the performance unit (PMNC) of the Cortex A8 has
> > some serious bug, in short the performance counters overflow IRQ is to be
> > avoided. The solution I am implementing is to read and reset the counters
> > from a work queue that is triggered by a timer.
>
> Regarding this oprofile related part. I wonder how you can get oprofile
> working properly (providing non-bogus results) without performance
> counters overflow IRQ generation?
>
> Are you trying to implement (in a clean way) something similar to
> http://marc.info/?l=oprofile-list&m=123688347009580&w=2
>
> Or is it going to be a different workaround?
I am trying to get a different approach, starting from the errata description. 
The idea is to avoid the counters from overflowing, which could cause a PMNC 
unit reset or lock-up (or both).

Here are the implementation details:
- use a timer to read and reset the counters, then fire a work queue
- in the work queue the counters values are converted to oprofile samples
- the proper locking is used to avoid some races between the various tasks

I am nearly done with it but I am now running into problems with PM 
(suspend/resume) and get_irq_regs().

What do you think?
How far are you on your side? Did you stress test the solution? Is the PMNC 
recovery always successful?

Regards,
Jean

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