Messages in this thread | ![/](/images/icornerl.gif) | | From | Mikael Pettersson <> | Date | Fri, 10 Jan 2003 08:05:07 +0100 | Subject | Re: detecting hyperthreading in linux 2.4.19 |
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James Cleverdon writes: > On Thursday 09 January 2003 12:02 pm, Jason Lunz wrote: > > Is there a way for a userspace program running on linux 2.4.19 to tell > > the difference between a single hyperthreaded xeon P4 with HT enabled > > and a dual hyperthreaded xeon P4 with HT disabled? The /proc/cpuinfos > > for the two cases are indistinguishable. > > > > Jason > > > > - > > In the kernel that's no problem: > > A) If the BIOS writers followed Intel's guidelines, just look at the physical > APIC IDs. HT siblings have odd IDs, the real ones have even. > > B) Check the siblings table built up at boot time and used by the scheduler. > > I don't know of any way to do this in userland. The whole point is that the > sibling processors are supposed to look like real ones.
If the kernel has sched_setaffinity() or some other way of binding a process to a given CPU (as numbered by the kernel, which may or may not be related to any physical CPU numbers), then this will do it: execute CPUID on each CPU and check the initial APIC ID field. If you find one that's non-zero, then HT is enabled.
My performance monitoring counters driver uses this approach in kernel-space using smp_call_function(). I don't use the siblings tables because they suck :-) [I don't think they distinguish between logical CPUs #0 and #1, and they aren't exported to modules. The CPUID check is simple and portable across kernel versions.] - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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