Category Archives: Hardware

HP ProBook 4540s brightness control in Ubuntu 13.10

The HP ProBook 4540s is a good choice when you need a GNU/Linux machine, but there are some hit and miss on the details. The thing I found most tedious is the brightness controls using the keyboard: they simply don’t work at all.

My soloution

See the kernel parameters actually used:

$ cat /proc/cmdline 
BOOT_IMAGE=/boot/vmlinuz-3.11.0-15-generic root=UUID=8850c025-676a-4e8c-ac83-4ed1147b88d4 ro quiet splash vt.handoff=7

If there’s no reference to acpi_backlight, that’s the problem. Add the parameter to /etc/default/grub changing the following line from

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

to

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"

Done

Debugging IO on Android

Android is Linux based, so there are some interesting way to monitor and debug IO activity especially on storage.

The one I found more useful is this:

  1. enable dumping of IO info
    echo 1 > /proc/sys/vm/block_dump
  2. observe kernel log
    cat /proc/kmsg
  3. make your analysis
  4. disable dumping of IO info
    echo 0 > /proc/sys/vm/block_dump

The output you will get is similar to this:
<7>[71477.927886] kswapd0(24): WRITE block 21240712 on mmcblk0p12 (8 sectors)
<7>[71477.928436] kswapd0(24): WRITE block 21410792 on mmcblk0p12 (8 sectors)
<7>[71477.928710] kswapd0(24): WRITE block 21240704 on mmcblk0p12 (8 sectors)
<7>[71477.929016] kswapd0(24): WRITE block 21240656 on mmcblk0p12 (8 sectors)
<7>[71477.929443] kswapd0(24): WRITE block 25427968 on mmcblk0p12 (8 sectors)
<7>[71477.929687] kswapd0(24): WRITE block 8 on mmcblk0p12 (8 sectors)
<7>[71477.930084] kswapd0(24): WRITE block 0 on mmcblk0p12 (8 sectors)
<7>[71478.086639] sdcard(159): READ block 23431168 on mmcblk0p12 (256 sectors)
<7>[71478.087036] sdcard(159): READ block 23430912 on mmcblk0p12 (8 sectors)
<7>[71478.258148] sdcard(159): READ block 23430920 on mmcblk0p12 (200 sectors)
<7>[71478.258514] sdcard(159): READ block 23431424 on mmcblk0p12 (8 sectors)
<7>[71478.266967] sdcard(138): READ block 23430656 on mmcblk0p12 (32 sectors)
<7>[71478.268798] sdcard(159): READ block 23430688 on mmcblk0p12 (64 sectors)
<7>[71478.269409] sdcard(159): READ block 23430752 on mmcblk0p12 (128 sectors)
<7>[71478.271484] sdcard(159): READ block 23430880 on mmcblk0p12 (32 sectors)
<7>[71478.600646] sdcard(138): READ block 23431432 on mmcblk0p12 (512 sectors)
<7>[71478.765136] sdcard(159): READ block 23431944 on mmcblk0p12 (256 sectors)
<7>[71478.958129] Compiler(412): READ block 327320 on mmcblk0p11 (8 sectors)
<7>[71478.958557] Compiler(412): READ block 327400 on mmcblk0p11 (48 sectors)

Tried on my rooted Galaxy Nexus with CyanogenMod 10.1.0-RC1.