On Monday 29 June 2009 19:54:23 Siarhei Siamashka wrote: > 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-dr >iver-for-oprofile-p21374285.html All right, sorry I was not aware of that discussion. So the PMNC unit is broken beyond repair. BTW good description and test results! > > 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. Ok. It looks like it is the best we can do. Thanks, Jean -- 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
