On 17.02.2010, at 17:34, Avi Kivity wrote: > On 02/17/2010 06:23 PM, Alexander Graf wrote: >> On 17.02.2010, at 17:03, Avi Kivity wrote: >> >> >>> On 02/17/2010 04:56 PM, Alexander Graf wrote: >>> >>>> So I changed to code according to your input by making all FPU calls >>>> explicit, getting rid of all binary patching. >>>> >>>> On the PowerStation again I'm running this code (simplified to the >>>> important instructions) using kvmctl: >>>> >>>> li r2, 0x1234 >>>> std r2, 0(r1) >>>> lfd f3, 0(r1) >>>> lfd f4, 0(r1) >>>> do_mul: >>>> fmul f0, f3, f4 >>>> b do_mul >>>> >>>> >>>> With the following kvm_stat output: >>>> >>>> dec 2236 53 >>>> exits 60797802 1171403 >>>> ext_intr 379 4 >>>> halt_wakeup 0 0 >>>> inst_emu 60795247 1171344 >>>> ld 60795132 1171348 >>>> >>>> So I'm getting 1171403 fmul operations per second. And that's even with >>>> non-optimized instruction fetching. Not bad. >>>> >>>> >>> It's a large number, but won't real hardware be three orders of magnitude >>> faster? >>> >> Yes, it would. But we don't have to care. The only thing we need to worry >> about is being fast enough to emulate enough FPU instructions actually used >> in normal guests so the guest runs in full speed. And 1000k> 250k, so we >> can do that apparently, leaving some spare cycles for non-fpu instructions. >> > > I'm sure 250k isn't representative of a floating point intensive program (but > maybe there aren't fpu intensive applications on that cpu).
Now you made me check how fast the real hw is. I get about 65,000,000 fmul operations per second on it. So we're 65x slower on a PowerStation. And that's for a tight FPU only loop. I'm still not convinced we're running into major problems. Alex-- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
