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Increasing Hard Drive Performance Under Linux on a Test Agent Machine

 Technote (troubleshooting)
 
This document applies only to the following language version(s):
English
 
Problem(Abstract)
The environment of a performance test should be as controlled as possible which means that there should not be any performance lags on the IBM Rational Test Agent machine(s). Lag on the test agent machine may produce false negatives.
 
Cause
The source of Hard Drive lag can vary. However most likely its from DMA issues.
 
Resolving the problem
To make sure that there is no lag from the hard drive, one should invoke hdparm. To test your hard drive use the following command:

hdparm -tT /dev/<hard drive device>

This will result in a performance test of your hard drive like the following:


/dev/hda:
Timing buffer-cache reads: 128 MB in 1.34 seconds =95.52 MB/sec
Timing buffered disk reads: 64 MB in 17.86 seconds = 3.58 MB/sec

In order to improve this check your settings with the following:

hdparm /dev/<hard drive device>

/dev/hda:
multcount = 0 (off)
I/O support = 0 (default 16-bit)
unmaskirq = 0 (off)
using_dma = 0 (off)
keepsettings = 0 (off)
nowerr = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 1870/255/63, sectors = 30043440, start = 0

Which means the following:

  • multcount: Short for multiple sector count. This controls how many sectors are fetched from the disk in a single I/O interrupt. Almost all modern IDE drives support this. The man page claims:

    When this feature is enabled, it typically reduces operating system overhead for disk I/O by 30-50%. On many systems, it also provides increased data throughput of anywhere from 5% to 50%.

  • I/O support: This flag controls how data is passed from the PCI bus to the controller.

  • unmaskirq: Turning this on will allow Linux to unmask other interrupts while processing a disk interrupt. It lets Linux attend to other interrupt-related tasks (i.e., network traffic) while waiting for your disk to return with the data it asked for. It should improve overall system response time, but be warned: Not all hardware configurations will be able to handle it. See the manpage.

  • using_dma: DMA mode, although most BIOSs should do this for you at boot time. Using DMA nearly always gives the best performance, with fast I/O throughput and low CPU usage.

    Now to speed things up add 32-bit I/O support (-c3), Multicount (-m16), unmasking interrupts (-u1), DMA (d1), Set the transfermode to udma (-X43, -X66, etc..).

    hdparm -X66 -d1 -u1 -m16 -c3 /dev/hda

    /dev/hda:
    setting 32-bit I/O support flag to 3
    setting multcount to 16
    setting unmaskirq to 1 (on)
    setting using_dma to 1 (on)
    setting xfermode to 66 (UltraDMA mode2)
    multcount = 16 (on)
    I/O support = 3 (32-bit w/sync)
    unmaskirq = 1 (on)
    using_dma = 1 (on)

    Running "hdparm -tT /dev/<Hard Disk Device>" should return better results.

    hdparm -tT /dev/hda

    /dev/hda:
    Timing buffer-cache reads: 128 MB in 1.43 seconds =89.51 MB/sec
    Timing buffered disk reads: 64 MB in 3.18 seconds =20.13 MB/sec

    Results will vary based on Hardware,




    Do you need more help?

    For additional assistance, contact IBM Rational Client Support:
    Submit a Service Request (SR)
    •  
     
    Cross Reference information
    Segment Product Component Platform Version Edition
    Software DevelopmentRational Test AgentDocumentationLinux2003.06.00, 2003.06.10, 2003.06.12, 2003.06.13, 2003.06.14, 2003.06.15, 2003.06.16, 7.0, 7.0.1
     
     

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    Document information

    Product categories:

    Software

    Software Development

    Software Quality Management

    Rational TestManager

    Test Agent

    Operating system(s):

    Linux

    Software version:

    7.0, 7.0.0.1, 7.0.0.2, 7.0.0.3, 7.0.0.4, 7.0.1, 7.0.1.1, 7.0.1.2, 7.0.1.3, 7.0.2, 2003.06.00, 2003.06.10, 2003.06.12, 2003.06.13, 2003.06.14, 2003.06.15, 2003.06.16

    Reference #:

    1168592

    IBM Group:

    Software Group

    Modified date:

    2008-12-18

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