Dave Hansen wrote: > On Sun, 2007-07-08 at 11:14 +0300, Avi Kivity wrote: > >> Dave Hansen wrote: >> >>> I've noticed that some of my tests run *MUCH* slower in kvm-28 than in >>> 27. I'm sure that wall time is pretty wonky in the guests, but it is >>> much slower in real-world time as well. >>> >>> Here's a little test to create a 32MB zeroed file with dd. Here it is >>> from kvm-27 (this took ~5.5 seconds on my wristwatch): >>> 33554432 bytes transferred in 0.052050 seconds (644657845 bytes/sec) >>> 33554432 bytes transferred in 0.062933 seconds (533176451 bytes/sec) >>> >>> Here's the same thing from kvm-28 (~80 seconds on my wristwatch): >>> 33554432 bytes transferred in 38.607065 seconds (869127 bytes/sec) >>> 33554432 bytes transferred in 22.274318 seconds (1506418 bytes/sec) >>> >>> Same host kernel, same kvm kernel modules (from kvm-28) same guest >>> kernel, same command-line options, same disk image. >>> >>> Any ideas what is going on? >>> >>> >> Is this repeatable? I don't see anything in kvm-27..kvm-28 that >> warrants such a regression. >> > > Right now, it's completely repeatable > > >> Things to check: >> >> - effect of pinning the vm onto one cpu (with 'taskset') >> > > Tried this. No effect that I can see at all. > > >> - does any counter in kvm_stat behave differently >> > > Nothing really stands out. The most strange thing to me is that the > counters are very stationary on the slow one. It doesn't look like it > is spinning on something, just that it is idle. Its counters during the > dd look very much like the guest does when it is idle: >
What does 'top' on the host show in both cases? There was a change in kvm userspace that affected IDE. Can you try kvm-27 userspace with a kvm-28 kernel module? If that's slow, then the only recourse is bisecting. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
