Fast Virtio VM
This page explains a way to build a blazing fast Gentoo VM under KVM using Virtio and mdev.
Use a fast computer
No really, this is probably the most important thing of all, don't expect a 2 second booting VM if you are on a P3 with a slow IDE disk. This tutorial is Build on a CentOS 6.2 KVM HypverVisor on a Dual QuadCore Xeon 2.4Ghz with 8 (v)CPU's and 2GB RAM assigned to the VM. The disk file is on an SSD (old Intel x25-M 80GB, so there is more to gain if you use a faster SSD).
It has the fastest mount time.
Compile the kernel with:
- VirtIO support
- Hugetlb support
- NO usb support (Unless planning to passthrough USB from the host).
- NO HID support (see above).
- NO extended video/device drivers/filesystem drivers that will not be used. (duh)
- NO fuse support (Slow...)
- NO modules (Slower...)
Kernel boot options
- noapic (APIC is for hardware management, and since we are in VM and the hardware is managed by our host, we don't need it).
- notsc (TSC is CPU clock synchronization, not needed in a VM).
Because they cannot be removed from the kernel itself, no need these as kernel boot options.
Use a static IP
DHCP is slow.
Replace udev with mdev (BusyBox), udev is dead slow vs mdev.
Remove useless mdev devices (tun,tap, all sound, hd*, sd*, fd*, md*, grsec(*), zap, dvb, v4l stuff)
Prelink all binaries:
emerge --ask prelink
Use rc-update to delete all non-essential daemons (git, consolefont, devfs, keymaps, modules, sysfs, swclock, staticroute)
Use tmpfs for /tmp and /var/run (will not necessarily speedup boot, but for startup services that /tmp heavily, it might help).
I created my own boot time init script, which echoes the current kernel uptime.
Please keep in mind that all of this is without *any* dirty tricks like initrd or initramfs. It's just static sequential boot.
Even using parallel start of services (thru
RC_PARALLEL="yes") would slow down the system.