Re: [Qemu-arm] [RFC PATCH v2 1/2] utils: Add helper to read arm MIDR_EL1 register

[Vijay Kilari]

On Thu, Aug 18, 2016 at 2:20 PM, Paolo Bonzini <address@hidden> 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. 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.
>