On Monday 29 June 2009 19:37:57 Russell King - ARM Linux wrote: > 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. I think it is possible, well if you except the get_irq_regs() problem. The idea is to read and reset the counters before the overflow, instead of loading them with a small negative value and waiting for the overflow to happen. > 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. The errata is about a lost event and/or a lock-up of the PMNC unit at the time of overflow. > I think just accepting that this erratum breaks oprofile is the only > realistic solution. ;( Completely agree. However it would be nice to have a workaround, as un-elegant as it can be ;( -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
