Re: [Qemu-devel] [PATCH] target-arm: Use common CPU cycle infrastructure

[Peter Crosthwaite]

On Fri, Oct 2, 2015 at 9:56 AM, Peter Maydell <address@hidden> wrote:
> On 2 October 2015 at 17:44, Christopher Covington <address@hidden> wrote:
>> I've sent out the CPI test case and while exercising it I noticed that
>> Laurent's patch fixed -icount. So my original goal has been accomplished. I'm
>> happy to rebase this patch if the authorities (Peter Maydell?) think using
>> cpu_get_ticks() is the right thing to do. Otherwise I'll probably try to move
>> on to support for the instructions event in the ARM PMU.
>
> Authority here is probably Peter Crosthwaite. I can produce an
> opinion but I'd have to go and research a bunch of stuff to do
> that, so I'm hoping to avoid it...
>

So my idea here is the CPU input frequency should be a property of the CPU.

Some experimental results confirm that the PMCCNTR on many common ARM
implementations is directly connected to the input clock and can be
relied on as a straight free-running counter. I think a genuine
instruction counter is something else and this timer should be
independent of any core provider of cycle count.

Regards,
Peter

> thanks
> -- PMM