On 18/08/2016 11:01, Vijay Kilari wrote:
> On Thu, Aug 18, 2016 at 2:20 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
>>
>>
>> On 18/08/2016 09:56, Vijay Kilari wrote:
>>> The get_aarch_cpu_id() has check " if (unlikely(!cpu_info_read)) ".
>>> If we call get_aarch_cpu_id() from is_thunderx_pass2_cpu() which is
>>> called from inside the loop, we will be adding one additional check.
>>
>> On the other hand, you are making an assumption that the caller of
>> is_thunderx_pass2_cpu() calls get_aarch64_cpu_id() first, and not
>> documenting it anywhere.
>>
>> And given that you shouldn't call _any_ function from inside such a hot
>> loop, your solution is inferior on both counts.
>
> Yes, but I could not think of better way to get rid of this check.
bool need_aa64_prefetch = is_thunderx_pass2();
for (...) {
if (need_aa64_prefetch) {
...
}
}
The check on cpu_info_read is done just once.
Paolo
However
> as Richard suggested (in another email), to drop this check and let prefetch
> be called for all the arm64 architectures. But I don't have any other
> arm64 platform
> to check the impact of it.
>
>>
>> Paolo
>>
>>> What I observed is having extra check inside the loop is adding 100 to
>>> 200ms overhead
>>> on live migration time. So I added this variable extra is_thunderx_cpu
>>> static variable
>>> to make it simple single check.
>>
