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mfcking
Beginner
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Help: L2 cache load hit rate is negative in the sampling data.

I collected some sampling data for kernel functions in Linux kernel 2.6.9 using VTune RDC, I found one hotspot function even has a negative L2 load hit rate (-37.289), it does have very high L2 cache miss per instruction (1.373) though. Is that possible?

Thanks,

L.Y.

Message Edited by mfcking@yahoo.com on 06-10-2005 09:57 AM

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4 Replies
72 Views

Never seen it myself: sounds like utterly bogus data.
mfcking
Beginner
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So why does VTune create this utterly bogus data? A bug for VTune? The data for other hotspot functions seem normal.
TimP
Black Belt
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In my experience, it means one of your sampling sessions didn't complete properly. Could be almost anything; out of disk space, lan connection interrupted,... The developers are so perfect in their setup that they never see this.
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The key here is that supported environments are listed out in detail in the product release notes. Intel THOROUGHLY tests VTune in those specific environments, which is why we urge users to stick to them.
If you're exploring newterritory, the software may or may not work --like every application on the planet: surely we can agree this is not a VTune-specific quirk. Applications always list the environments that they can be expected to work in, and VTune is no exception.
The known and unknown variations out in the market over the past 5 years say, of and withinOS distributions -- kernel, glibc, glibc++, etc etc etc --mixed with the released processors at the time would create a staggeringly large test and support matrix, most of which would likely not even be of interest to our user base. That's why we target specific distributions, and also why our support of newer releases takes some time.
Occasionally our customers are interested in the newer OS environments, or sometimes less popular ones, before we are able to update our software to accomodate them. Since the remote agent (vtserver) is a lean, mean profiling machine, typically it supports new environments before vtl/vtlec does.
One of the important functions of this forum is to help Intel hear when we're missing the mark, and conversations like this threadare SUPER important to us towards learning how we can do better.
jdg

Message Edited by jdgallag on 06-11-2005 10:12 AM

Message Edited by jdgallag on 06-11-2005 10:27 AM

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