Commit f2521c90 authored by Peter Lieven's avatar Peter Lieven Committed by Stefan Hajnoczi
Browse files

qemu-img: dynamically adjust iobuffer size during convert 



since the convert process is basically a sync operation it might
be benificial in some case to change the hardcoded I/O buffer
size to a greater value.

This patch increases the I/O buffer size if the output
driver advertises an optimal transfer length or discard alignment
that is greater than the default buffer size of 2M.

Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarPeter Lieven <pl@kamp.de>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 7572ddc8

qemu-img.c

+13 −3
Original line number Diff line number Diff line
@@ -1140,6 +1140,7 @@ static int img_convert(int argc, char **argv) 
            sector_num_next_status = 0;

    uint64_t bs_sectors;

    uint8_t * buf = NULL;

    size_t bufsectors = IO_BUF_SIZE / BDRV_SECTOR_SIZE;

    const uint8_t *buf1;

    BlockDriverInfo bdi;

    QEMUOptionParameter *param = NULL, *create_options = NULL;
@@ -1398,7 +1399,16 @@ static int img_convert(int argc, char **argv) 
    bs_i = 0;

    bs_offset = 0;

    bdrv_get_geometry(bs[0], &bs_sectors);

    buf = qemu_blockalign(out_bs, IO_BUF_SIZE);



    /* increase bufsectors from the default 4096 (2M) if opt_transfer_length

     * or discard_alignment of the out_bs is greater. Limit to 32768 (16MB)

     * as maximum. */

    bufsectors = MIN(32768,

                     MAX(bufsectors, MAX(out_bs->bl.opt_transfer_length,

                                         out_bs->bl.discard_alignment))

                    );



    buf = qemu_blockalign(out_bs, bufsectors * BDRV_SECTOR_SIZE);



    if (skip_create) {

        int64_t output_length = bdrv_getlength(out_bs);
@@ -1421,7 +1431,7 @@ static int img_convert(int argc, char **argv) 
            goto out;

        }

        cluster_size = bdi.cluster_size;

        if (cluster_size <= 0 || cluster_size > IO_BUF_SIZE) {

        if (cluster_size <= 0 || cluster_size > bufsectors * BDRV_SECTOR_SIZE) {

            error_report("invalid cluster size");

            ret = -1;

            goto out;
@@ -1558,7 +1568,7 @@ static int img_convert(int argc, char **argv) 
                sector_num_next_status = sector_num + n1;

            }



            n = MIN(nb_sectors, IO_BUF_SIZE / 512);

            n = MIN(nb_sectors, bufsectors);

            n = MIN(n, bs_sectors - (sector_num - bs_offset));

            n1 = n;