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    SubjectRe: General question (scheduler) with SSDs?


    On Fri, 20 Feb 2009, Sitsofe Wheeler wrote:

    > Whoops, I didn't mean to send that previous half formed mail :) Sorry.
    >
    > As mentioned in another mail there was a discussion on
    > http://lkml.org/lkml/2009/1/31/28 and long thread talking about the
    > introduction of the rotational flag here
    > http://lkml.org/lkml/2009/1/5/340 . Cheapo SSDs or even USB keys are not
    > auto detected as non-rotational devices by the kernel and after a bit of
    > poking about I've come up with the following udev rules for my
    > particular cases:
    >
    > SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{model}=="ASUS-PHISON *", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
    > SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{idVendor}=="0951", ATTRS{idProduct}=="1606", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
    > SUBSYSTEM=="block", TEST=="/sys$devpath/queue/rotational", ATTRS{manufacturer}=="SanDisk", ATTRS{product}=="Cruzer Micro", RUN+="/bin/sh -c 'echo 0 > /sys$devpath/queue/rotational'"
    >
    > Ever since the rotational option appeared I've been trying cfq but prior
    > to that I was using noop or deadline. However it doesn't look like
    > anyone has sat down and run the numbers to see what affect the
    > ioscheulder/rotational flag is having on cheapo SSDs - all the
    > suggestions are anecdotal. Could you run some benchmarks with these
    > different options and report back the results?
    >
    > --
    > Sitsofe | http://sucs.org/~sits/
    >

    $ grep rotational -r /usr/src/linux/
    /usr/src/linux/drivers/scsi/NCR5380.c: * USLEEP_POLL should be a maximum rotational latency.
    /usr/src/linux/fs/partitions/sun.c: __be16 rspeed; /* Disk rotational speed */
    /usr/src/linux/fs/ufs/ufs_fs.h: * Compute the cylinder and rotational position of a cyl block addr.
    /usr/src/linux/fs/ufs/ufs_fs.h: __fs32 fs_nrpos; /* number of rotational positions */
    /usr/src/linux/fs/ufs/ufs_fs.h:#define UFS_42POSTBLFMT -1 /* 4.2BSD rotational table format */
    /usr/src/linux/fs/ufs/ufs_fs.h:#define UFS_DYNAMICPOSTBLFMT 1 /* dynamic rotational table format */
    /usr/src/linux/fs/ufs/ufs_fs.h: __s32 s_nrpos; /* number of rotational positions */
    /usr/src/linux/include/linux/blkdev.h:#define QUEUE_FLAG_NONROT 14 /* non-rotational device (SSD) */
    /usr/src/linux/include/linux/genhd.h: __u16 d_rpm; /* rotational speed */

    # find /sys/|grep -i rotational
    #

    Which kernel{option} do you enable to enable support for that option in /sys?

    Justin.



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