Re: [Qemu-devel] [PATCH v6 11/14] target/arm: PMU: Add instruction and cycle events

[Richard Henderson]

On 10/17/18 12:47 PM, Aaron Lindsay wrote:
> On Oct 16 17:04, Richard Henderson wrote:
>> On 10/10/18 1:37 PM, Aaron Lindsay wrote:
>>> + * Return the underlying cycle count for the PMU cycle counters. If we're 
>>> in
>>> + * usermode, simply return 0.
>>> + */
>>> +static uint64_t cycles_get_count(CPUARMState *env)
>>> +{
>>> +#ifndef CONFIG_USER_ONLY
>>> +    return muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL),
>>> +                   ARM_CPU_FREQ, NANOSECONDS_PER_SECOND);
>>> +#else
>>> +    return 0;
>>> +#endif
>>> +}
>>
>> Usually we pass through the host cycle counter.
>> See cpu_get_host_ticks().
> 
> Why do you prefer cpu_get_host_ticks()? And are you suggesting this for
> just user-mode, or both system and user?

Just user-mode.  Providing a clock with unknown scaling is more useful than a
constant 0.


r~