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 your kernel with:
- VirtIO support
- Hugetlb support
- NO usb support (Unless you plan to passthrough USB from the host).
- NO HID support (see above).
- NO extended video/device drivers/filesystem drivers you don't use. (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 f* slow.
Remove useless mdev devices (tun,tap, all sound, hd*, sd*, fd*, md*, grsec(*), zap, dvb, v4l stuff)
Prelink all binaries, (emerge prelink -> prelink -amRf)
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 necesarrily speedup boot, but if you have startup services that use /tmp heavilly, it might help).
I created my own boottime 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.