I'm using Ubuntu Server 12.04 LTS on a AMD E-350 based machine. During I/O heavy loads (for example transferring files via NFS or HTTP, extracting archives, making backups etc.) the CPU load goes completly insane. I saw load averages well above eight on this two core machine... and the responsiveness is much lower.

I think the issues are definitely on the kernel side of things, but see for yourself:

$ sudo hdparm -I /dev/sdb

/dev/sdb:



ATA device, with non-removable media

    Model Number:       SAMSUNG HD501LJ                             

    Firmware Revision:  CR100-10

    Transport:          Serial, ATA8-AST, SATA 1.0a, SATA II Extensions, SATA Rev 2.5

Standards:

    Used: ATA-8-ACS revision 3b 

    Supported: 8 7 6 5 

Configuration:

    Logical        max    current

    cylinders    16383    16383

    heads        16    16

    sectors/track    63    63

    --

    CHS current addressable sectors:   16514064

    LBA    user addressable sectors:  268435455

    LBA48  user addressable sectors:  976771055

    Logical/Physical Sector size:           512 bytes

    device size with M = 1024*1024:      476938 MBytes

    device size with M = 1000*1000:      500106 MBytes (500 GB)

    cache/buffer size  = 16384 KBytes (type=DualPortCache)

Capabilities:

    LBA, IORDY(can be disabled)

    Queue depth: 32

    Standby timer values: spec'd by Standard, no device specific minimum

    R/W multiple sector transfer: Max = 16    Current = 16

    Recommended acoustic management value: 254, current value: 128

    DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6 udma7 

         Cycle time: min=120ns recommended=120ns

    PIO: pio0 pio1 pio2 pio3 pio4 

         Cycle time: no flow control=120ns  IORDY flow control=120ns

Commands/features:

    Enabled    Supported:

       *    SMART feature set

            Security Mode feature set

       *    Power Management feature set

       *    Write cache

       *    Look-ahead

       *    Host Protected Area feature set

       *    WRITE_BUFFER command

       *    READ_BUFFER command

       *    NOP cmd

       *    DOWNLOAD_MICROCODE

            SET_MAX security extension

       *    Automatic Acoustic Management feature set

       *    48-bit Address feature set

       *    Device Configuration Overlay feature set

       *    Mandatory FLUSH_CACHE

       *    FLUSH_CACHE_EXT

       *    SMART error logging

       *    SMART self-test

       *    General Purpose Logging feature set

       *    64-bit World wide name

       *    Segmented DOWNLOAD_MICROCODE

       *    Gen1 signaling speed (1.5Gb/s)

       *    Gen2 signaling speed (3.0Gb/s)

       *    Native Command Queueing (NCQ)

       *    Host-initiated interface power management

       *    Phy event counters

       *    DMA Setup Auto-Activate optimization

            Device-initiated interface power management

       *    Software settings preservation

       *    SMART Command Transport (SCT) feature set

       *    SCT Long Sector Access (AC1)

       *    SCT LBA Segment Access (AC2)

       *    SCT Error Recovery Control (AC3)

       *    SCT Features Control (AC4)

       *    SCT Data Tables (AC5)

Security: 

    Master password revision code = 65534

        supported

    not    enabled

    not    locked

        frozen

    not    expired: security count

        supported: enhanced erase

    168min for SECURITY ERASE UNIT. 168min for ENHANCED SECURITY ERASE UNIT.

Logical Unit WWN Device Identifier: 50000f001b301090

    NAA        : 5

    IEEE OUI    : 0000f0

    Unique ID    : 01b301090

Checksum: correct

$ iostat 1 # One slice below

Device:            tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn

sda               0.00         0.00         0.00          0          0

sdb             355.00     60544.00         0.00      60544          0

$ vmstat 1

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----

 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa

 1  9      0 152864     12 3302740    0    0 61952     0 18115 1999  1 24 12 63

 0  8      0 153316     12 3302060    0    0 59648     0 20060 2393  1 33  9 57

 0 10      0 153432     12 3302060    0    0 54784     0 18430 2205  1 24 11 65

 1  8      0 154848     12 3301216    0    0 59392     0 19011 2291  1 31  8 60

 0  9      0 149676     12 3306324    0    0 59392     0 21149 2417  2 29  6 64

 0  9      0 150460     12 3305268    0    0 61952     0 18664 2117  1 28 11 60

 1  8      0 152084     12 3304028    0    0 59392     0 20045 2245  2 31  6 62

 1  8      0 152548     12 3303452    0    0 60160     0 20105 2426  2 29  9 60

Anything I could do about that?