Avi Kivity wrote: > On 02/08/2010 12:02 AM, Alexander Graf wrote: >> >>> It's not a good idea for the kernel either, if it happens all the >>> time. If a typical Gekko application uses the fpu and the emulated >>> instructions intensively, performance will suck badly (as in: qemu/tcg >>> will be faster). >>> >>> >> Yeah, I haven't really gotten far enough to run full-blown guests yet. >> So far I'm on demos and they look pretty good. >> >> But as far as intercept speed goes - I just tried running this little >> piece of code in kvmctl: >> >> .global _start >> _start: >> li r3, 42 >> mtsprg 0, r3 >> mfsprg r4, 0 >> b _start >> >> and measured the amount of exits I get on my test machine: >> >> processor : 0 >> cpu : PPC970MP, altivec supported >> clock : 2500.000000MHz >> revision : 1.1 (pvr 0044 0101) >> >> ---> >> >> exits 1811108 >> >> I have no idea how we manage to get that many exits, but apparently we >> are. So I'm less concerned about the speed of the FPU rerouting at the >> moment. >> > > That's pretty impressive (never saw x86 with this exit rate) but it's > more than 1000 times slower than the hardware, assuming 1 fpu IPC (and > the processor can probably do more). An fpu intensive application > will slow to a crawl. Measuring a typical Gekko application, I get about 200k-250k of fpu (incl. paired singles) instructions per second. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
