Messages in this thread | | | Date | Mon, 10 Nov 2008 07:39:22 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes |
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Ingo Molnar wrote: > * Alexander van Heukelum <heukelum@fastmail.fm> wrote: > > hackbench is _way_ too noisy to measure such cycle-level differences > as irq entry changes cause. It also does not really stress interrupts > - it only stresses networking, the VFS and the scheduler. > > a better test might have been to generate a ton of interrupts, but > even then it's _very_ hard to measure it properly. The best method is > what i've suggested to you early on: run a loop in user-space and > observe irq costs via RDTSC, as they happen. Then build a histogram > and compare the before/after histogram. Compare best-case results as > well (the first slot of the histogram), as those are statistically > much more significant than a noisy average. >
For what it's worth, I tested this out, and I'm pretty sure you need to run a uniprocessor configuration (or system) for it to make sense -- otherwise you end up missing too many of the interrupts. I first tested this on an 8-processor system and, well, came up with nothing.
I'm going to try this later on a uniprocessor, unless Alexander beats me to it.
-hpa
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