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    Subject[PATCH RFC 0/2] percpu_tags: Prototype implementation
    Date
    Hello Gentleman,

    This is a development of "percpu_ida" library. I named it
    "percpu_tags" to simplify review, since most of "percpu_ida"
    code has gone and a diff would not be informative.

    While the concept of per-cpu arrays is is preserved, the
    implementation is heavily reworked. The main objective is to
    improve the "percpu_ida" locking scheme.

    Here is the list of major differrences between "percpu_ida" and
    "percpu_tags":

    * The global freelist has gone. As result, CPUs do not compete
    for the global lock.

    * Long-running operatons (scanning thru a cpumask) are executed
    with local interrupts enabled;

    * percpu_ida::percpu_max_size limit is eliminated. Instead, the
    limit is determined dynamically. Depending from how many CPUs
    are requesting tags each CPU gets a fair share of the tag space;

    * A tag is attempted to return to the CPU it was allocated on. As
    result, it is expected the locality of data associated with the
    tag benefits;

    The code is largely raw and untested. The reason I am posting
    is the prototype implementation performs 2-3 times faster than
    "percpu_ida", so I would like to ensure if it worth going further
    with this approach or is there a no-go.

    The performance test is not decent, though. I used "fio" random
    read against a "null_blk" device sitting on top of "percpu_tags",
    which is not exactly how "percpu_ida" is used. This is another
    reason I am posting - an advice on how to properly test is very
    appreciated.

    The source code could be found at
    https://github.com/a-gordeev/linux.git percpu_tags-v0

    Thanks!

    Cc: linux-scsi@vger.kernel.org
    Cc: qla2xxx-upstream@qlogic.com
    Cc: Nicholas Bellinger <nab@daterainc.com>
    Cc: Kent Overstreet <kmo@daterainc.com>
    Cc: "Michael S. Tsirkin" <mst@redhat.com>

    Alexander Gordeev (2):
    percpu_tags: Prototype implementation
    percpu_tags: Use percpu_tags instead of percpu_ida

    drivers/scsi/qla2xxx/qla_target.c | 6 +-
    drivers/target/iscsi/iscsi_target_util.c | 6 +-
    drivers/target/target_core_transport.c | 4 +-
    drivers/target/tcm_fc/tfc_cmd.c | 8 +-
    drivers/vhost/scsi.c | 6 +-
    include/linux/percpu_tags.h | 37 ++
    include/target/target_core_base.h | 4 +-
    lib/Makefile | 2 +-
    lib/percpu_tags.c | 556 ++++++++++++++++++++++++++++++
    9 files changed, 611 insertions(+), 18 deletions(-)
    create mode 100644 include/linux/percpu_tags.h
    create mode 100644 lib/percpu_tags.c

    --
    1.7.7.6



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