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    Subject[PATCH 02/16] GFS2: Speed up gfs2_rbm_from_block
    Date
    From: Bob Peterson <rpeterso@redhat.com>

    This patch is a rewrite of function gfs2_rbm_from_block. Rather than
    looping to find the right bitmap, the code now does a few simple
    math calculations.

    I compared the performance of both algorithms side by side and the new
    algorithm is noticeably faster. Sample instrumentation output from a
    "fast" machine:

    5 million calls: millisec spent: Orig: 166 New: 113
    5 million calls: millisec spent: Orig: 189 New: 114

    In addition, I ran postmark (on a somewhat slowr CPU) before the after
    the new algorithm was put in place and postmark showed a decent
    improvement:

    Before the new algorithm:
    -------------------------
    Time:
    645 seconds total
    584 seconds of transactions (171 per second)

    Files:
    150087 created (232 per second)
    Creation alone: 100000 files (2083 per second)
    Mixed with transactions: 50087 files (85 per second)
    49995 read (85 per second)
    49991 appended (85 per second)
    150087 deleted (232 per second)
    Deletion alone: 100174 files (7705 per second)
    Mixed with transactions: 49913 files (85 per second)

    Data:
    273.42 megabytes read (434.08 kilobytes per second)
    852.13 megabytes written (1.32 megabytes per second)

    With the new algorithm:
    -----------------------
    Time:
    599 seconds total
    530 seconds of transactions (188 per second)

    Files:
    150087 created (250 per second)
    Creation alone: 100000 files (1886 per second)
    Mixed with transactions: 50087 files (94 per second)
    49995 read (94 per second)
    49991 appended (94 per second)
    150087 deleted (250 per second)
    Deletion alone: 100174 files (6260 per second)
    Mixed with transactions: 49913 files (94 per second)

    Data:
    273.42 megabytes read (467.42 kilobytes per second)
    852.13 megabytes written (1.42 megabytes per second)

    Signed-off-by: Bob Peterson <rpeterso@redhat.com>
    Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

    diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
    index 3d469d3..24bb0b8 100644
    --- a/fs/gfs2/incore.h
    +++ b/fs/gfs2/incore.h
    @@ -621,6 +621,7 @@ struct gfs2_sbd {
    u32 sd_hash_bsize_shift;
    u32 sd_hash_ptrs; /* Number of pointers in a hash block */
    u32 sd_qc_per_block;
    + u32 sd_blocks_per_bitmap;
    u32 sd_max_dirres; /* Max blocks needed to add a directory entry */
    u32 sd_max_height; /* Max height of a file's metadata tree */
    u64 sd_heightsize[GFS2_MAX_META_HEIGHT + 1];
    diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
    index e443966..0e3554e 100644
    --- a/fs/gfs2/ops_fstype.c
    +++ b/fs/gfs2/ops_fstype.c
    @@ -278,6 +278,9 @@ static int gfs2_read_sb(struct gfs2_sbd *sdp, int silent)
    sdp->sd_qc_per_block = (sdp->sd_sb.sb_bsize -
    sizeof(struct gfs2_meta_header)) /
    sizeof(struct gfs2_quota_change);
    + sdp->sd_blocks_per_bitmap = (sdp->sd_sb.sb_bsize -
    + sizeof(struct gfs2_meta_header))
    + * GFS2_NBBY; /* not the rgrp bitmap, subsequent bitmaps only */

    /* Compute maximum reservation required to add a entry to a directory */

    diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
    index 38fe18f..669b89b 100644
    --- a/fs/gfs2/rgrp.c
    +++ b/fs/gfs2/rgrp.c
    @@ -251,22 +251,25 @@ static u32 gfs2_bitfit(const u8 *buf, const unsigned int len,
    static int gfs2_rbm_from_block(struct gfs2_rbm *rbm, u64 block)
    {
    u64 rblock = block - rbm->rgd->rd_data0;
    - u32 goal = (u32)rblock;
    - int x;
    + u32 x;

    if (WARN_ON_ONCE(rblock > UINT_MAX))
    return -EINVAL;
    if (block >= rbm->rgd->rd_data0 + rbm->rgd->rd_data)
    return -E2BIG;

    - for (x = 0; x < rbm->rgd->rd_length; x++) {
    - rbm->bi = rbm->rgd->rd_bits + x;
    - if (goal < (rbm->bi->bi_start + rbm->bi->bi_len) * GFS2_NBBY) {
    - rbm->offset = goal - (rbm->bi->bi_start * GFS2_NBBY);
    - break;
    - }
    - }
    + rbm->bi = rbm->rgd->rd_bits;
    + rbm->offset = (u32)(rblock);
    + /* Check if the block is within the first block */
    + if (rbm->offset < (rbm->bi->bi_start + rbm->bi->bi_len) * GFS2_NBBY)
    + return 0;

    + /* Adjust for the size diff between gfs2_meta_header and gfs2_rgrp */
    + rbm->offset += (sizeof(struct gfs2_rgrp) -
    + sizeof(struct gfs2_meta_header)) * GFS2_NBBY;
    + x = rbm->offset / rbm->rgd->rd_sbd->sd_blocks_per_bitmap;
    + rbm->offset -= x * rbm->rgd->rd_sbd->sd_blocks_per_bitmap;
    + rbm->bi += x;
    return 0;
    }

    --
    1.7.4


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