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
