On May 6, 2015 10:22 AM, "Ingo Molnar" <[email protected]> wrote: > > > * Andy Lutomirski <[email protected]> wrote: > > > On May 5, 2015 11:30 PM, "Ingo Molnar" <[email protected]> wrote: > > > > > > Add a short FPU performance suite that runs once during bootup. > > > > > > It can be enabled via CONFIG_X86_DEBUG_FPU_PERFORMANCE=y. > > > > Neat! > > > > Can you change "cycles" to "TSC ticks"? They're not quite the same thing. > > Yeah, with constant TSC we have the magic TSC frequency that is used > by RDTSC. > > I'm torn: 'TSC ticks' will mean very little to most people reading > that output. We could convert it to nsecs with a little bit of > calibration - but that makes it depend on small differences in CPU > model frequencies, while the (cached) cycle costs are typically > constant per microarchitecture.
Isn't it dependent on the ratio of max turbo frequency to TSC freq? Typical non-ultra-mobile systems should be at or near max turbo frequency during bootup. > > I suspect we could snatch a performance counter temporarily, to get > the real cycles count, and maybe even add a uops column. Most of this > needs to run in kernel space, so it's not a tooling project. This will suck under KVM without extra care. I know, because I'm working on a similar userspace tool that uses RDPMC. Another option would be rdmsr(MSR_IA32_APERF), but that isn't available under KVM either. > > I also wanted to add cache-cold numbers which are very interesting as > well, just awfully hard to measure in a stable fashion. For cache-cold > numbers the natural unit would be memory bus cycles. Yeah, maybe it's worth wiring up perf counters at some point. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
