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? -- error compiling committee.c: too many arguments to function -- 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
