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
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