Re: [PATCH v14 00/11] KVM: x86/pmu: Guest Last Branch Recording Enabling

[Like Xu]

On 30/7/2021 11:15 am, Liuxiangdong wrote:
> Hi, like.
>
> Does it have requirement on CPU if we want to use LBR in Guest?

As long as you find valid output from the "dmesg| grep -i LBR" like 
"XX-deep LBR",
you can use LBR on the host and theoretically on the most Intel guest.

But I don't have various Intel machine types for testing.

As far as I know, the guest LBR doesn't work on the platforms that
the MSR_LBR_SELECT is defined per physical core not logical core.

I will fix this issue by making KVM aware of the recent core scheduling 
policy.

> I have tried linux-5.14-rc3 on different CPUs. And I can use lbr on 
> Haswell, Broadwell, skylake and icelake, but I cannot use lbr on IvyBridge.

I suppose INTEL_FAM6_IVYBRIDGE and INTEL_FAM6_IVYBRIDGE_X do support LBR.

You may check the return values from x86_perf_get_lbr() or
cpuid_model_is_consistent() in the KVM for more details.

> Thanks!
>
>
> On 2021/7/29 20:40, Liuxiangdong wrote:
> > Hi, like.
> >
> > This patch set has been merged in 5.12 kernel tree so we can use LBR 
> > in Guest.
> > Does it have requirement on CPU?
> > I can use lbr in guest on skylake and icelake, but cannot on IvyBridge.
> >
> > I can see lbr formats(000011b) in perf_capabilities msr(0x345), but 
> > there is still
> > error when I try.
> >
> > $ perf record -b
> > Error:
> > cycles: PMU Hardware doesn't support sampling/overflow-interrupts. Try 
> > 'perf stat'
> >
> > Host CPU:
> > Architecture:                    x86_64
> > CPU op-mode(s):                  32-bit, 64-bit
> > Byte Order:                      Little Endian
> > Address sizes:                   46 bits physical, 48 bits virtual
> > CPU(s):                          24
> > On-line CPU(s) list:             0-23
> > Thread(s) per core:              2
> > Core(s) per socket:              6
> > Socket(s):                       2
> > NUMA node(s):                    2
> > Vendor ID:                       GenuineIntel
> > CPU family:                      6
> > Model:                           62
> > Model name:                      Intel(R) Xeon(R) CPU E5-2620 v2 @ 
> > 2.10GHz
> > Stepping:                        4
> >
> >
> > Thanks!
> > Xiangdong Liu