Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?

[Richard W.M. Jones]

On Tue, Aug 03, 2010 at 02:33:02PM +0300, Gleb Natapov wrote:
> On Tue, Aug 03, 2010 at 12:13:06PM +0100, Richard W.M. Jones wrote:
> > 
> > qemu compiled from today's git.  Using the following command line:
> > 
> > $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios \
> >     -drive file=/dev/null,if=virtio \
> >     -enable-kvm \
> >     -nodefaults \
> >     -nographic \
> >     -serial stdio \
> >     -m 500 \
> >     -no-reboot \
> >     -no-hpet \
> >     -net user,vlan=0,net=169.254.0.0/16 \
> >     -net nic,model=ne2k_pci,vlan=0 \
> >     -kernel /tmp/libguestfsEyAMut/kernel \
> >     -initrd /tmp/libguestfsEyAMut/initrd \
> >     -append 'panic=1 console=ttyS0 udevtimeout=300 noapic acpi=off 
> > printk.time=1 cgroup_disable=memory selinux=0 
> > guestfs_vmchannel=tcp:169.254.2.2:35007 guestfs_verbose=1 TERM=xterm-color '
> > 
> > With kernel 2.6.35 [*], this takes about 1 min 20 s before the guest
> > starts.
> > 
> > If I revert back to kernel 2.6.34, it's pretty quick as usual.
> > 
> > strace is not very informative.  It's in a loop doing select and
> > reading/writing from some file descriptors, including the signalfd and
> > two pipe fds.
> > 
> > Anyone seen anything like this?
> > 
> I assume your initrd is huge.

It's ~110MB, yes.

> In newer kernels ins/outs are much slower that they were. They are
> much more correct too. It shouldn't be 1 min 20 sec for 100M initrd
> though, but it can take 20-30 sec. This belongs to kvm list BTW.

I can't see anything about this in the kernel changelog.  Can you
point me to the commit or the key phrase to look for?

Also, what's the point of making in/out "more correct" when they we
know we're talking to qemu (eg. from the CPUID) and we know it already
worked fine before with qemu?

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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