vince, On Mon, Mar 2, 2015 at 2:31 PM, Vince Weaver <vincent.weaver@xxxxxxxxx> wrote: > > On Sun, 1 Mar 2015, Stephane Eranian wrote: > > > You need to describe your test better. Are you saying that the register values > > you were seeing with REGS_USER, REGS_INTR, precise_ip > 0 are all > > the same? That is certainly not impossible. If your PMU interrupts are all > > at the user level, then REGS_INTR = REGS_USER. With precise_ip > 0, > > you will get the machine state on retirement of the sampled instruction. > > But if you have no sampling skid without precise_ip, then both states > > the REGS_INTR and REGS_INTR+precise_ip>0 could be identical. > > If you enable both PERF_SAMPLE_REGS_USER and PERF_SAMPLE_REGS_INTR > then you will get in the PERF_RECORD_SAMPLE results for both user > and intr. However they will be identical, always, because > the kernel code just checks if PERF_SAMPLE_REGS_INTR was given and > then returns the PEBS state for both. > If the PMU interrupt occurred at the user level, then this makes sense. both perf_sample_regs_user() and perf_sample_regs_intr() use the same pt_regs() which has the user state. I think your comment is more along the lines that REGS_USER should not receive PEBS machine state. Problem is that there is only one set of pt_regs passed to __intel_pmu_pebs_event(). And if REGS_INTR is set, then the pt_regs registers are indeed overwritten with PEBS captured state. To avoid the issue, we would have to carry around two sets of pt_regs. > My test was expecting that if you specified PERF_SAMPLE_REGS_USER and > PERF_SAMPLE_REGS_INTR then for the PERF_SAMPLE_REGS_USER values you'd > get the same results as when PERF_SAMPLE_REGS_INTR were not specified, but > that's not the case. > This could certainly be fixed with two sets of pt_regs to make the results more consisten when REGS_USER and REGS_INTR + precise are used. > > This is an obscure corner case, but I found the results unexpected. > > Vince -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
