Messages in this thread | | | Date | Thu, 13 Nov 2008 17:18:21 -0800 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH RFC/RFB] x86_64, i386: interrupt dispatch changes |
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Matt Mackall wrote: > On Mon, 2008-11-10 at 21:00 -0800, H. Peter Anvin wrote: >> Okay, after spending most of the day trying to get something that isn't >> completely like white noise (interesting problem, otherwise I'd have >> given up long ago) I did, eventually, come up with something that looks >> like it's significant. I did a set of multiple runs, and am looking for >> the "waterfall points" in the cumulative statistics. >> >> http://www.zytor.com/~hpa/baseline-hpa-3000-3600.pdf >> >> This particular set of data points was gathered on a 64-bit kernel, so I >> didn't try the segment technique. >> >> It looks to me that the collection of red lines is enough to the left of >> the black ones that one can assume there is a significant effect, >> probably by about a cache miss worth of time. > > This graph is a little confusing. Is the area under each curve here > supposed to be a constant? >
No, they reflect individual runs. They start at 1 at the top left and drop to 0 at the far right in each case. What matters is the horizontal position of large vertical drops.
> Is this latency from all interrupts as seen by userspace? Or does a > particular interrupt dominate? >
All interrupts, but rather inherently the difference between interrupt handlers is going to be bigger than the differences between implementations of the same handler. I *believe* all the interrupts you're seeing in that graph are probably timer interrupts. The other major interrupt source that was active on the system was USB.
-hpa
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