Floating point vs Integer performance
I ran some benchmarks inside of KVM-12 on my system and outside of KVM (no virtualization on my system). I found that floating point performance when running both with and without KVM was approximately the same, but integer performance in KVM was about 25% of what I get when running the test outside of KVM. These were tests using Dhrystone 2 and Double Precision Whetstone on a Core 2 Duo T7200 processor.
Any thoughts on why the integer and floating point performance appears to differ so much?
Benjamin Prosnitz
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Quoted 11 lines · Benjamin Prosnitz
I ran some benchmarks inside of KVM-12 on my system and outside of KVM (no virtualization on my system). I found that floating point performance when running both with and without KVM was approximately the same, but integer performance in KVM was about 25% of what I get when running the test outside of KVM. These were tests using Dhrystone 2 and Double Precision Whetstone on a Core 2 Duo T7200 processor.
Any thoughts on why the integer and floating point performance appears to differ so much?
Perhaps the integer benchmarks thrash the mmu cache. Try raising KVM_NUM_MMU_PAGES to 1024.
4MB per VM lowmem is a lot, but if it helps many workloads, it's worth it.
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Hi!
Quoted 9 lines · Benjamin Prosnitz
I ran some benchmarks inside of KVM-12 on my system and outside of KVM (no virtualization on my system). I found that floating point performance when running both with and without KVM was approximately the same, but integer performance in KVM was about 25% of what I get when running the test outside of KVM. These were tests using Dhrystone 2 and Double Precision Whetstone on a Core 2 Duo T7200 processor.
Any thoughts on why the integer and floating point performance appears to differ so much?
I guess it's the benchmark. In contrast to its FP counterpart, Dhrystone doesn't crunch numbers most of the time. It also performs lots of string operations, for example (memory access == slow).
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