Re: [PATCH v3 3/9] KVM: x86: Add Intel Processor Trace virtualization mode

[Paolo Bonzini]

On 27/11/2017 21:23, Luwei Kang wrote:
> +/* Default is host guest mode. */
> +static int __read_mostly pt_mode = PT_MODE_HOST_GUEST;
> +module_param(pt_mode, int, S_IRUGO);
> +

This will cause a slowdown on new processors.  Please make the default
PT_SYSTEM until that is addressed (with a combination of XSAVES, caching
the host rtit_ctl at the kernel level, or something like that).

Paolo