Re: [Starpu-devel] [selective access mode setting]

[Maxim Abalenkov <maxim.abalenkov@gmail.com>]

Dear Samuel,

Thank you very much for your help. Can you please verify that I’m using the flag correctly? Please take a look at the below code snippet:

void core_starpu_zgetrf_pnl(plasma_desc_t A, struct starpu_data_descr dSeg,
                            plasma_pivot_t p, int u, int ldau, int ib, int prio)
{
    // Pointer to first tile in panel
    struct starpu_data_descr *dTile = plasma_tile_desc(A, 0, 0);

    // Set access modes for tiles in panel
     dTile->mode         = STARPU_RW;  // first
    (dTile+A.mt-1)->mode = STARPU_RW;  // last

    // middle
    for (int i = 1; i < A.mt-1; i++) {
        (dTile+i)->mode = STARPU_R;

        // @test
        starpu_data_set_sequential_consistency_flag((dTile+i)->handle, 0);
    }

    // Set access mode for pivots segment
    dSeg.mode = STARPU_W;

    int retval = starpu_task_insert(
       &core_starpu_codelet_zgetrf_pnl,
        STARPU_VALUE,               &A,         sizeof(plasma_desc_t),
        STARPU_DATA_MODE_ARRAY,      dTile,     A.mt,
        STARPU_DATA_MODE_ARRAY,     &dSeg,      1,
        STARPU_VALUE,               &p,         sizeof(plasma_pivot_t),
        STARPU_VALUE,               &u,         sizeof(int),
        STARPU_VALUE,               &ldau,      sizeof(int),
        STARPU_VALUE,               &ib,        sizeof(int),
        STARPU_PRIORITY,             prio,
        STARPU_NAME,               "zgetrf_pnl",
        0);

    STARPU_CHECK_RETURN_VALUE(retval,
            "core_starpu_zgetrf_pnl: starpu_task_insert() failed");

    // @test: middle
    for (int i = 1; i < A.mt-1; i++) {
        starpu_data_set_sequential_consistency_flag((dTile+i)->handle, 1);
    }
}

Here I am disabling and re-enabling the sequential data consistency for the intermediate matrix tiles (not the first and the last). What I would like to achieve is to disable dependency tracking for one particular task and then re-enable it. Is that possible? Am I doing it correctly?

—

Best wishes,

Maxim

Maxim Abalenkov \\ maxim.abalenkov@gmail.com
+44 7 486 486 505 \\ http://mabalenk.gitlab.io

On 6 Sep 2018, at 17:12, Samuel Thibault <samuel.thibault@inria.fr> wrote:

Maxim Abalenkov, le jeu. 06 sept. 2018 17:06:31 +0100, a ecrit:

Pass the first and the last data handles with STARPU_RW access modes and all
the intermediate handles as the normal STARPU_VALUE without any dependence
tracking. Would that work?

My mission is to simplify the DAG. I feel/believe too many (unnecessary)
dependencies slow down my code.

If the goal is to drop dependency tracking, you can simply disable
sequential consistency  for these data with
starpu_data_set_sequential_consistency_flag.

Normally, dependency tracking uses O(1) algorithms so it shouldn't be
too costly, but it's not harm checking if that's the case :)

Samuel