Gautam, Thanks for this patch
Gautam Menghani <gau...@linux.ibm.com> writes: > Currently, on a P10 KVM guest, the mitigations seen in the output of > "lscpu" command are different from the host. The reason for this > behaviour is that when the KVM guest makes the "h_get_cpu_characteristics" > hcall, QEMU does not consider the data it received from the host via the > KVM_PPC_GET_CPU_CHAR ioctl, and just uses the values present in > spapr->eff.caps[], which in turn just contain the default values set in > spapr_machine_class_init(). > > Fix this behaviour by making sure that h_get_cpu_characteristics() > returns the data received from the KVM ioctl for a KVM guest. > > Perf impact: > With null syscall benchmark[1], ~45% improvement is observed. > > 1. Vanilla QEMU > $ ./null_syscall > 132.19 ns 456.54 cycles > > 2. With this patch > $ ./null_syscall > 91.18 ns 314.57 cycles > > [1]: https://ozlabs.org/~anton/junkcode/null_syscall.c > > Signed-off-by: Gautam Menghani <gau...@linux.ibm.com> > --- <snip> LGTM, Reviewed-by: Vaibhav Jain <vaib...@linux.ibm.com> -- Cheers ~ Vaibhav
