OSDL aio-stress results on latest kernels show buffered random read issue

From: Judith Lebzelter (judith_at_osdl.org)
Date: 09/30/04

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    Date:	Wed, 29 Sep 2004 16:29:08 -0700 (PDT)
To: <linux-aio@kvack.org>

    Hello;

    I am running aio-stress on the most recent kernels and have
    found that on linux-2.6.8, 2.6.9-rc2 and 2.6.9-rc2-mm4 the
    performance of buffered random reads is poor compared to the
    buffered random writes:

                   2.6.8 2.6.9-rc2 2.6.9-rc2-mm4
                 --------------------------------------------
    random write 35.66 MB/s 34.80 MB/s 29.89 MB/s
    random read 7.69 MB/s 7.50 MB/s 7.68 MB/s

    ** 2CPU hosts with striped Megaraid. 1G RAM. 4G File.

    This shows up on our 4CPU host as well. (striped AACRAID.4G
    RAM. 8G File):
                 2.6.9-rc2 2.6.9-rc2-mm4 2.6.9-rc2-mm1
                 -------------------------------------------
    random write 31.36 MB/s 18.92 MB/s 18.97 MB/s
    random read 11.13 MB/s 9.74 MB/s 11.05 MB/s

    There seems to be an issue with the reads. Usually, reads
    should be at least as fast as writes of the same type.

    Also, there seems to be a substantial drop-off in the performance
    of AIO buffered-random writes in the mm kernels. (14% on 2CPU,
    40% on 4CPU)

    Regards;
    Judith Lebzelter
    OSDL

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