On 05/04/2014 11:40 AM, Ingo Molnar wrote:
>
> * Andy Lutomirski <l...@amacapital.net> wrote:
>
>>> That said, regular *device* interrupts do often return to kernel
>>> mode (the idle loop in particular), so if you have any way to
>>> measure that, that might be interesting, and might show some of
>>> the same advantages.
>>
>> I can try something awful involving measuring latency of
>> hardware-timed packets on a SolarFlare card, but I'll have
>> calibration issues. I suppose I could see if 'ping' gets faster.
>> In general, this will speed up interrupts that wake userspace from
>> idle by about 100ns on my box, since it's presumably the same size
>> and the speedup per loop in my silly benchmark.
>
> To simulate high rate device IRQ you can generate very high frequency
> lapic IRQs by using hrtimers, that's generating a ton of per CPU lapic
> IRQs.
>
The bigger question is if that helps in measuring the actual latency.
It should get more data points, to be sure.
Maybe let userspace sit in a tight loop doing RDTSC, and look for data
points too far apart to have been uninterrupted?
-hpa
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