hyperv/hv: use MSR to hint hypervisor on entering idle.

[howard0su_gmail.com]

mismerge one line, add it back

[sepherosa_gmail.com]

sys/dev/hyperv/vmbus/hv_hv.c

521

Hmm, we should make the test more stringent:

if ((hyperv_features & HV_FEATURE_MSR_GUEST_IDLE) &&
    (hyperv_features3 & HV_FEATURE3_GUEST_IDLE))

522

Well, does it really work for you? acpi_cpu will override cpu_idle_hook unconditionally later.

[howard0su_gmail.com]

sys/dev/hyperv/vmbus/hv_hv.c

522

I set the breakpoint in DDB to make sure it works. I believe acpi_cpu is earlier.

[sepherosa_gmail.com]

sys/dev/hyperv/vmbus/hv_hv.c

522

I added a log in hyperv_init() and acpi_cpu_startup(), see the last line in the two log chunks.

...
Apr 18 09:57:02 perf01-sephe kernel: FreeBSD clang version 3.8.0 (tags/RELEASE_380/final 262564) (based on LLVM 3.8.0)
Apr 18 09:57:02 perf01-sephe kernel: Hyper-V Version: 6.3.9600 [SP18]
Apr 18 09:57:02 perf01-sephe kernel: Features=0xe7f<VPRUNTIME,TMREFCNT,SYNIC,SYNTM,APIC,HYPERCALL,VPINDEX,REFTSC,IDLE,TMFREQ>
Apr 18 09:57:02 perf01-sephe kernel: PM Features=max C2, 0x0
Apr 18 09:57:02 perf01-sephe kernel: Features3=0x17b2<DEBUG,XMMHC,IDLE,NUMA,TMFREQ,SYNCMC,CRASH,NPIEP>
Apr 18 09:57:02 perf01-sephe kernel: Timecounter "Hyper-V" frequency 10000000 Hz quality 10000000
Apr 18 09:57:02 perf01-sephe kernel: hyperv init
...
...
...
Apr 18 09:57:02 perf01-sephe kernel: sc0: VGA <16 virtual consoles, flags=0x300>
Apr 18 09:57:02 perf01-sephe kernel: vga0: <Generic ISA VGA> at port 0x3c0-0x3df iomem 0xa0000-0xbffff on isa0
Apr 18 09:57:02 perf01-sephe kernel: Timecounters tick every 1.000 msec
Apr 18 09:57:02 perf01-sephe kernel: acpi_cpu override idle hook
...

I think you were adding the ddb brkptr to the MSR idle routing; the MSR version would be triggered before the ACPI cpu overrides, but it does not mean ACPI cpu takes over the idle hook earlier.

[howard0su_gmail.com]

This need more testing and some change in my private tree is dependency for this change.