Re: [Qemu-arm] [RFC PATCH v2 2/3] utils: Add cpuinfo helper to fetch /proc/cpuinfo

[Peter Maydell]

On 7 April 2016 at 11:56, Vijay Kilari <address@hidden> wrote:
> On Thu, Apr 7, 2016 at 3:41 PM, Peter Maydell <address@hidden> wrote:
>> On 7 April 2016 at 10:58,  <address@hidden> wrote:
>>> From: Vijaya Kumar K <address@hidden>
>>>
>>> utils cannot read target cpu information to
>>> fetch cpu information to implement cpu specific
>>> features or erratas. For this parse /proc/cpuinfo
>>> and fetch cpu information.
>>>
>>> For now this helper only fetches cpu information
>>> for arm architectures.
>>
>> As I understand it /proc/cpuinfo is intended only for
>> humans to read. Please don't write code to parse it;
>> find a different way to get this information instead
>> if you really need it.

> Also unlike x86 there is no cpuid.h where we can get cpu identification
> information for arm64.

I'm told there are kernel patches in progress to get this sort
of information in a maintainable way to userspace, which are
currently somewhat stalled due to lack of anybody who wants to
consume it. If you have a use case then you should probably
flag it up with the kernel devs.

That said, I think we should probably hold off on this
discussion until we have clearer benchmarking info that
demonstrates that doing these prefetches really does make
a significant difference. I would much prefer to have a
single aarch64 routine that works for everybody, rather
than a thunderx-only special case.

thanks
-- PMM