On Mon, Aug 29, 2016 at 02:30:46AM +0530, Madhavan Srinivasan wrote: > It's a perennial request from hardware folks to be able to > see the raw values of the pmu registers. Partly it's so that > they can verify perf is doing what they want, and some > of it is that they're interested in some of the more obscure > info that isn't plumbed out through other perf interfaces.
How much and what is that? Can't we try and get interfaces sorted? > Over the years internally have used various hack to get > the requested data out but this is an attempt to use a > somewhat standard mechanism (using PERF_SAMPLE_REGS_INTR). Not really liking that. It assumes too much and doesn't seem to cover about half the perf use-cases. It assumes the machine state can be captured by registers (this is false for things like Intel DS/PT, which have state in memory), it might assume <= 64 registers but I didn't look that closely, this too might become somewhat restrictive. Worse, it doesn't work for !sampling workloads, of which you also very much want to verify programming etc. > This would also be helpful for those of us working on the perf > hardware backends, to be able to verify that we're programming > things correctly, without resorting to debug printks etc. On x86 we can trace the MSR writes. No need to add debug printk()s. We could (and I have on occasion) added tracepoints (well trace_printk) to the Intel DS memory stores to see what was written there. Tracing is much more flexible for debugging this stuff. Can't you do something along those lines?
