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: http://www.nabble.com/Re%3A--PATCH-0-1--OMAP-gptimer-based-event-monitor-driver-for-oprofile-p21374285.html > 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 -- 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
