I could only find an advisory (regarding sr-iov and irq remaps) from HP to RHEL6.2 users stating that Gen8 firmware does not enable it by default.
http://h20564.www2.hp.com/hpsc/doc/public/display?docId=emr_na-c03645796 """ The interrupt remapping capability depends on x2apic enabled in the BIOS and HP ProLiant Gen8 systems do not enable x2apic; therefore, the following workaround is required for device assignment: Edit the /etc/grub.conf and add intremap=no_x2apic_optout option to the kernel command line options. """ Probably for backwards compatibility... not sure if there is an option to enable/disable it in firmware (like DL390 seems to have). I don't think so... but I was told by HP team that I should use x2apic for >= Gen8. On Thu, Feb 19, 2015 at 2:59 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Thu, Feb 19, 2015 at 8:32 AM, Rafael David Tinoco <ina...@ubuntu.com> > wrote: >> Feb 19 08:21:28 derain kernel: [ 3.637682] Switched APIC routing to >> cluster x2apic. > > Ok. That "cluster x2apic" mode is just about the nastiest mode when it > comes to sending a single ipi. We do that insane dance where we > > - turn single cpu number into cpumask > - copy the cpumask to a percpu temporary storage > - walk each cpu in the cpumask > - for each cpu, look up the cluster siblings > - for each cluster sibling that is also in the cpumask, look up the > logical apic mask and add it to the actual ipi destination mask > - send an ipi to that final mask. > > which is just insane. It's complicated, it's fragile, and it's unnecessary. > > If we had a simple "send_IPI()" function, we could do this all with > something much saner, and it would look sopmething like > > static void x2apic_send_IPI(int cpu, int vector) > { > u32 dest = per_cpu(x86_cpu_to_logical_apicid, cpu); > x2apic_wrmsr_fence(); > __x2apic_send_IPI_dest(dest, vector, APIC_DEST_LOGICAL); > } > > and then 'void native_send_call_func_single_ipi()' would just look like > > void native_send_call_func_single_ipi(int cpu) > { > apic->send_IPI(cpu, CALL_FUNCTION_SINGLE_VECTOR); > } > > but I might have missed something (and we might want to have a wrapper > that says "if the apic doesn't have a 'send_IPI' function, use > "send_IPI_mask(cpumask_of(cpu, vector) instead" > > The fact that you need that no_x2apic_optout (which in turn means that > your ACPI tables seem to say "don't use x2apic") also makes me worry. > > Are there known errata for the x2apic? > > Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
