Re: [PATCH 2/5] KVM: Implement CR read caching for KVM paravirt_ops

Anthony Liguori
2007-06-18T12:27:25Z

Avi Kivity wrote:
> Anthony Liguori wrote:
>> +/*
>> + * Control register reads can be trapped. Since trapping is relatively
>> + * expensive, we can avoid paying the cost by caching logically.
>> + */
>> +static unsigned long kvm_read_cr(int reg)
>> +{
>> + struct kvm_paravirt_state *state
>> + = per_cpu(paravirt_state, smp_processor_id());
>> +
>> + if (unlikely(!state->cr_valid[reg])) {
>> + if (reg == 0)
>> + state->cached_cr[reg] = native_read_cr0();
>> + else if (reg == 3)
>> + state->cached_cr[reg] = native_read_cr3();
>> + else if (reg == 4)
>> + state->cached_cr[reg] = native_read_cr4();
>> + else
>> + BUG();
>> + state->cr_valid[reg] = 1;
>> + }
>> + return state->cached_cr[reg];
>> +}
>> +
>
> It would be good to declare this (and kvm_write_cr) always_inline.
> These functions are never called with a non-constant reg parameters,
> and the unsightly if tree (more readable as a switch, IMO) will fold
> nicely when inlined.

Ok.

Regards,

Anthony Liguori