>On Mon, Feb 12, 2007 at 05:21:26AM -0800, Dor Laor wrote: >> >> >> >> >hi, >> >> > Can someone briefly explain what the cr3-cache feature on intel >> VT >> >> >processors is and how it is used to improve performance in >> >> >paravirtualization. >> >> >> >> In short, this is a unique Intel VT feature that supposed to save >> vmexit >> >> on cr3 switch. The vmexit operation is quite expensive at the moment >> >> (something like 2-5 ms!). PV kernels can use this feature by sharing >> > ^^^^^^^^^^^^^^^^^^^^^^^^ >> > >> >Where do you measured this unbelievable large number? On AMD-V I >> >measured around 2400 processor cycles for a VMEXIT/VMENTRY roundtrip. I >> >would really really wonder if Intel-VT is that slow... >> >> Intel is indeed slower than AMD with this one. >> I didn't measure such roundtrip specifically. We usually see that the >> VMETNRY/VMEXIT cycle limits our performance (for io/mmio,..) >> On Intel core duo we cannot get more than 150k-200k VMEXITS per second >> for regular guest doing extensive IO. >> >> Anyway 2ms for a 2.4G processor equals 4800 cycles so it's not that far. > > Hum, ms means millisecond in the SI system, so on a 2.4 billion cycle/s >2ms would be 4.8 million cycles, hence IMHO the unbelievably large >perception. >I assume you mean VMEXITS would be around 2-5 microsecond, which would fit >quite better in the overall picture :-)
Thanks man, my mistake, I meant microsecond when wrote the 'ms'. >Daniel > >-- >Red Hat Virtualization group http://redhat.com/virtualization/ >Daniel Veillard | virtualization library http://libvirt.org/ >[EMAIL PROTECTED] | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ >http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/ ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier. Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ kvm-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kvm-devel
