On Mon, Jun 29, 2009 at 07:36:57PM +0300, Siarhei Siamashka wrote: > On Monday 29 June 2009 17:31:18 ext Jean Pihet wrote: > > 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?
I don't think you can - triggering capture on overflow is precisely how oprofile works. The erratum talks about polling for overflow. By doing this, you are in a well defined part of the kernel, which is obviously going to be shown as a hot path for every counter, thus making oprofile useless for kernel work. Deferring the interrupt to a workqueue doesn't resolve the problem either. The problem has nothing to do with what happens after the interrupt occurs - it's about interrupts themselves being lost. I think just accepting that this erratum breaks oprofile is the only realistic solution. ;( -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
