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    Subject[PATCH] Re: linux readahead setting?
    Date
    On Tuesday 13 November 2001 16:21, Roy Sigurd Karlsbakk wrote:
    > Hi
    >
    > I heard linux does <= 32 page readahead from block devices
    > (scsi/ide/que?). Is there a way to double this? I want to read 256kB
    > chunks from the SCSI drives, as to get the best speed. These numbers are
    > based on some testing and information I've got from Compaq's storage guys.
    >
    > roy

    Note that the interface to /proc/ide/hdX/settings still is buggy...

    i.e you should be able to do (in pages):
    echo "file_readahead:64" > /proc/ide/hdX/settings
    but the result will be a readahead of 128*1024 PAGES... and that
    is too much... (even 1024 PAGES is too much)

    (after patch, in kB)
    echo "file_readahead:256" > /proc/ide/hdX/settings

    It is likely that there are more settings in the ide subsystem that is
    has this fault... (Andre, I keep repeating myself...)

    /RogerL
    --
    Roger Larsson
    Skellefteå
    Sweden
    *******************************************
    Patch prepared by: roger.larsson@norran.net
    Name of file: /home/roger/patches/patch-2.4.11-pre2-ide_settings

    --- linux/drivers/ide/ide-disk.c.orig Tue Oct 2 01:05:41 2001
    +++ linux/drivers/ide/ide-disk.c Thu Oct 4 21:15:36 2001
    @@ -690,7 +690,7 @@
    ide_add_setting(drive, "multcount", id ? SETTING_RW : SETTING_READ, HDIO_GET_MULTCOUNT, HDIO_SET_MULTCOUNT, TYPE_BYTE, 0, id ? id->max_multsect : 0, 1, 2, &drive->mult_count, set_multcount);
    ide_add_setting(drive, "nowerr", SETTING_RW, HDIO_GET_NOWERR, HDIO_SET_NOWERR, TYPE_BYTE, 0, 1, 1, 1, &drive->nowerr, set_nowerr);
    ide_add_setting(drive, "breada_readahead", SETTING_RW, BLKRAGET, BLKRASET, TYPE_INT, 0, 255, 1, 2, &read_ahead[major], NULL);
    - ide_add_setting(drive, "file_readahead", SETTING_RW, BLKFRAGET, BLKFRASET, TYPE_INTA, 0, INT_MAX, 1, 1024, &max_readahead[major][minor], NULL);
    + ide_add_setting(drive, "file_readahead", SETTING_RW, BLKFRAGET, BLKFRASET, TYPE_INTA, 0, 4096, PAGE_SIZE, 1024, &max_readahead[major][minor], NULL);
    ide_add_setting(drive, "max_kb_per_request", SETTING_RW, BLKSECTGET, BLKSECTSET, TYPE_INTA, 1, 255, 1, 2, &max_sectors[major][minor], NULL);
    ide_add_setting(drive, "lun", SETTING_RW, -1, -1, TYPE_INT, 0, 7, 1, 1, &drive->lun, NULL);
    ide_add_setting(drive, "failures", SETTING_RW, -1, -1, TYPE_INT, 0, 65535, 1, 1, &drive->failures, NULL);
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