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

From: Andrew Morton (akpm_at_osdl.org)
Date: 09/30/04

  • Next message: Ram Pai: "Re: [PATCH/RFC] Simplified Readahead" 
    Date:	Wed, 29 Sep 2004 20:46:28 -0700
To: Judith Lebzelter <judith@osdl.org>

    Judith Lebzelter <judith@osdl.org> wrote:
    >
    > 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)
    >

    Well one would expect writes to be much faster than reads because writes
    usually do not involve performing physical I/O, and when pagecache
    writeback finally happens it has vastly more data to work with and hence
    can schedule I/O more efficiently.

    Unless you are using O_SYNC or fsync(), in which case ignore the above.

    The regression within random write performance is unexpected. Can you
    please provide a URL to the current version of the test tool, and a
    description of how you are invoking it? What sort of I/O system, what
    filesystem, etc.

    Thanks.
    -
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  • Next message: Ram Pai: "Re: [PATCH/RFC] Simplified Readahead"

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    • Re: OSDL aio-stress results on latest kernels show buffered random read issue
      ... > I am running aio-stress on the most recent kernels and have ... > performance of buffered random reads is poor compared to the ... To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ ...
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    • OSDL aio-stress results on latest kernels show buffered random read issue
      ... I am running aio-stress on the most recent kernels and have ... performance of buffered random reads is poor compared to the ... random write 35.66 MB/s 34.80 MB/s 29.89 MB/s ... send the line "unsubscribe linux-kernel" in ...
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