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    SubjectRe: 2.6.0 performance problems
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    On Tue, 2003-12-30 at 00:58, Thomas Molina wrote:
    > On Mon, 29 Dec 2003, Linus Torvalds wrote:
    >
    > >
    > >
    > > On Mon, 29 Dec 2003, Thomas Molina wrote:
    > > >
    > > > I just finished a couple of comparisons between 2.4 and 2.6 which seem to
    > > > confirm my impressions. I understand that the comparison may not be
    > > > apples to apples and my methods of testing may not be rigorous, but here
    > > > it is. In contrast to some recent discussions on this list, this test is
    > > > a "real world" test at which 2.6 comes off much worse than 2.4.
    > >
    > > Are you sure you have DMA enabled on your laptop disk? Your 2.6.x system
    > > times are very high - much bigger than the user times. That sounds like
    > > PIO to me.
    >
    > It certainly looks like DMA is enabled. Under 2.4 I get:
    >
    > [root@lap root]# hdparm /dev/hda
    >
    > /dev/hda:
    > multcount = 16 (on)
    > IO_support = 1 (32-bit)
    > unmaskirq = 1 (on)
    > using_dma = 1 (on)
    > keepsettings = 0 (off)
    > readonly = 0 (off)
    > readahead = 8 (on)
    > geometry = 2584/240/63, sectors = 39070080, start = 0
    >
    >
    > Under 2.6 I get:
    >
    > [root@lap root]# hdparm /dev/hda
    >
    > /dev/hda:
    > multcount = 16 (on)
    > IO_support = 1 (32-bit)
    > unmaskirq = 1 (on)
    > using_dma = 1 (on)
    > keepsettings = 0 (off)
    > readonly = 0 (off)
    > readahead = 256 (on)
    > geometry = 38760/16/63, sectors = 39070080, start = 0
    >

    Increase your readahead:

    # hdparm -a 8192 /dev/hda


    BTW: As we really do get this question a _lot_ of times, why
    don't the ide layer automatically set a higher readahead
    if there is enough cache on the drive or something?


    Thanks,

    --
    Martin Schlemmer
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