Hi Weijiang, On 23/1/2022 12:11 am, Yang Weijiang wrote:
KVM legacy LBR patches have been merged in kernel 5.12, this patchset is to expose the feature to guest from the perf capability MSR. Qemu can add LBR format in cpu option to achieve it, e.g., -cpu host,lbr-fmt=0x5,
Some older Intel CPUs may have lbr-fmt=LBR_FORMAT_32 (which is 0), would you help verify that KVM is supported on these platforms ? If so, how do we enable guest LBR form the QEMU side, w/ -cpu host,lbr-fmt=0x0 ?
the format should match host value in IA32_PERF_CAPABILITIES. Note, KVM legacy LBR solution accelerates guest perf performace by LBR MSR passthrough so it requires guest cpu model matches that of host's, i.e.,
Would you help add live migration support across host/guest CPU models when hosts at both ends have the same number of LBR entries and the same lbr-fmt ? Thanks, Like Xu
only -cpu host is supported. Change in v5: 1. This patchset is rebased on tip : 6621441db5 2. No functional change since v4.
