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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: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Peter Lieven 2013-11-27 11:07:06 +01:00 committed by Stefan Hajnoczi
parent 7572ddc8db
commit f2521c9023
1 changed files with 13 additions and 3 deletions
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16
qemu-img.c
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@ -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;