On Monday 29 June 2009 19:58:41 ext Jean Pihet wrote:
> 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?

Russel was the first to reply :)

But we also discussed this "hybrid model" some time ago, and there is a clear
counterexample where it fails:

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

I ended up just using a timer with high frequency of samples generation. it
works without hassle and is sufficient for the majority of cases.

Best regards,
Siarhei Siamashka
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