On Tue, Jul 19, 2011 at 12:14:36PM +0300, Avi Kivity wrote: > On 07/18/2011 11:16 PM, Michael Tokarev wrote: > >It all started by Svante Signell on IRC, see > >http://bugs.debian.org/634149 . The short story: > >running hurd guest image (on ide drive); when changing > >only host kernel from 2.6.32 to (in my case) 3.0.0-rc7, > >the i/o (especially write) speed of the guest reduces > >dramatically, as is host CPU usage. I used a cd-1.iso > >install image from the URL provided in the bugreport, > >http://people.debian.org/~sthibault/hurd-i386/installer/cdimage/ -- > >even installing packages is very significantly slower > >in current kernels than it was in 2.6.32. > > > >Typical kvm_stats output on 3.0.0 host kernel: > > > >kvm-18166 [001] 47471.398406: kvm_emulate_insn: 80000000:160750: f3 66 6f > >kvm-18166 [001] 47471.398406: kvm_pio: pio_write at 0x1f0 size 2 count 1 > >kvm-18166 [001] 47471.398407: kvm_userspace_exit: reason KVM_EXIT_IO (2) > >kvm-18166 [001] 47471.398408: kvm_entry: vcpu 0 > >kvm-18166 [001] 47471.398409: kvm_exit: reason EXIT_IOIO rip 0x160750 info 1f0012c 0 > > > > > >Gleb, Avi -- what we're missing here? > > > >It does not look like the problem we have with FreeBSD, > >this is apparently something different... > > Looks like hurd doesn't use DMA. Instead it uses rep/outsw, which > indeed has a performance regression - it now exits on every word > instead of on every sector. > > Gleb? > Yes, we are discussing this right now on IRC with Michael. This is exactly the case :( Hurd developers says that they support IDE DMA though. -- Gleb. -- 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
