Fedora 10 - Disk IO

Identifying heavy disk IO tasks and reducing IO helps to shorten the boot time on e.g. a Asus EeePC.

To measure IO, I installed a systemtap script to run as soon as rc.sysinit starts.

#! /usr/bin/env stap
# modified traceio.stp
# Copyright (C) 2007 Red Hat, Inc., Eugene Teo <eteo@redhat.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 as
# published by the Free Software Foundation.
#

global device_of_interest, dev, reads, writes, total_io

probe begin {
  /* Hack! Insert your MAJOR, MINOR of the 
     device you are interested in */
  device_of_interest = MKDEV(253, 1)
}

probe vfs.read.return {
        if (dev == device_of_interest)
        reads[execname()] += $return
}

probe vfs.write.return {
        if (dev == device_of_interest)
        writes[execname()] += $return
}

probe timer.s(1) {
    foreach (p in reads)
        total_io[p] = 0
    foreach (p in writes)
        total_io[p] = 0
    foreach (p in reads)
        total_io[p] += reads[p]
    foreach (p in writes)
        total_io[p] += 5 * writes[p]
    foreach(p in total_io- limit 10)
        printf("%15s r: %8d KiB w: %8d KiB\n",
            p, reads[p]/1024,
            writes[p]/1024)
        printf("\n")
    # Note we don't zero out reads, writes,
    # so the values are cumulative since the script started.
}

Because on a EeePC disk writes are very slow (5 times slower than reading) they are weighted with factor 5.

From rc.sysinit start to the gdm login screen, the top 5 IO tasks are on my Live-CD standard installation:

• modprobe: I wonder what happened to Jakub's modprobe speedup patches.
• setroubleshootd: should really be more lightweight and needs a cleanup.
• gconfd-2, xkbcomp: Behdad has currently been looking at the login process, which hopefully improved the situation a bit.
  
• rpcbind: will have to investigate, why it reads so much.

Now, if you want to improve Fedora's boot speed, here is a starting point.