Messages in this thread | | | Date | Sun, 04 May 2014 12:59:46 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [RFC/HACK] x86: Fast return to kernel |
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On 05/04/2014 11:40 AM, Ingo Molnar wrote: > > * Andy Lutomirski <luto@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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