On Tuesday, March 06, 2012 2:16:03 am Maninya M wrote: > Thank you. > How do we get hardware cpuid? > Can we change the number of CPUs available to the scheduler (in the > scheduler code) dynamically, say completely cutting off a specific cpu core > from being used at all?
The hardware cpuid is machine-dependent. If you are in the kernel, you can use PCPU_GET(apic_id) on x86 to get the local APIC ID. Other platforms have a similar per-CPU variable. As far as getting it from userland, we do not have a good way of getting it currently aside from scraping /var/run/dmesg.boot or using libkvm to grovel around in kernel variables. As far as offlining a CPU, we do not have a way to do that currently (though you can take it out of the default cpuset which will prevent user threads from using it). > On 5 March 2012 22:51, John Baldwin <[email protected]> wrote: > > > On Friday, March 02, 2012 2:20:00 am Maninya M wrote: > > > I was unable to get this information about the cpuid variable in the > > > scheduler source code. > > > How does cpuid get its value from the hardware? > > > > The cpuid is a software ID value assigned during boot. It is not > > directly related to any specific hardware IDs. > > > > > How is the CPUSTATES value obtained/changed with hardware in the source > > > code? > > > > Do you mean, does cp_time[] handle hardware changes (hotplug CPUs, etc.)? > > Currently that isn't supported, the kernel assumes the set of CPUs is > > static for a given boot's lifetime. > > > > -- > > John Baldwin > > > > > > -- > Maninya > -- John Baldwin _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[email protected]"
