Message ID | 1379425736-11326-8-git-send-email-pl@kamp.de |
---|---|
State | New |
Headers | show |
On 09/17/2013 07:48 AM, Peter Lieven wrote: > Signed-off-by: Peter Lieven <pl@kamp.de> > --- > block.c | 57 +++++++++++++++++++++++++++++++++++++++++---------------- > 1 file changed, 41 insertions(+), 16 deletions(-) > > diff --git a/block.c b/block.c > index 177720e..74ec342 100644 > --- a/block.c > +++ b/block.c > @@ -2660,28 +2660,53 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs, > BlockDriver *drv = bs->drv; > QEMUIOVector qiov; > struct iovec iov; > - int ret; > + int ret = 0; > > - /* TODO Emulate only part of misaligned requests instead of letting block > - * drivers return -ENOTSUP and emulate everything */ > + /* if no limit is specified in the BlockDriverState use a default > + * of 32768 512-byte sectors (16 MiB) per request. > + */ > + int max_write_zeroes = bs->max_write_zeroes ? bs->max_write_zeroes : 32768; Worth having a named constant instead of a magic number? > + while (nb_sectors > 0 && !ret) { > + > + if (ret == -ENOTSUP) { > + /* Fall back to bounce buffer if write zeroes is unsupported */ > + iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE; > + iov.iov_base = qemu_blockalign(bs, iov.iov_len); > + memset(iov.iov_base, 0, iov.iov_len); This allocates, clears, and frees iov.iov_len bytes of 0 every iteration through the loop. Can you hoist that so you only allocate the bounce buffer once, and then clean it up after the loop completes?
Am 19.09.2013 um 22:07 schrieb Eric Blake <eblake@redhat.com>: > On 09/17/2013 07:48 AM, Peter Lieven wrote: >> Signed-off-by: Peter Lieven <pl@kamp.de> >> --- >> block.c | 57 +++++++++++++++++++++++++++++++++++++++++---------------- >> 1 file changed, 41 insertions(+), 16 deletions(-) >> >> diff --git a/block.c b/block.c >> index 177720e..74ec342 100644 >> --- a/block.c >> +++ b/block.c >> @@ -2660,28 +2660,53 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs, >> BlockDriver *drv = bs->drv; >> QEMUIOVector qiov; >> struct iovec iov; >> - int ret; >> + int ret = 0; >> >> - /* TODO Emulate only part of misaligned requests instead of letting block >> - * drivers return -ENOTSUP and emulate everything */ >> + /* if no limit is specified in the BlockDriverState use a default >> + * of 32768 512-byte sectors (16 MiB) per request. >> + */ >> + int max_write_zeroes = bs->max_write_zeroes ? bs->max_write_zeroes : 32768; > > Worth having a named constant instead of a magic number? Its the only place where it is used. I can do that, but I would keep it in front of the function rather than at the top of block.h or even in block_int.h > >> + while (nb_sectors > 0 && !ret) { > >> + >> + if (ret == -ENOTSUP) { >> + /* Fall back to bounce buffer if write zeroes is unsupported */ >> + iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE; >> + iov.iov_base = qemu_blockalign(bs, iov.iov_len); >> + memset(iov.iov_base, 0, iov.iov_len); > > This allocates, clears, and frees iov.iov_len bytes of 0 every iteration > through the loop. Can you hoist that so you only allocate the bounce > buffer once, and then clean it up after the loop completes? I can do that, but in this case, I have to allocate max_write_zeroes * BDRV_SECTOR_SIZE bytes because the iov_len might not be maximal in the first iteration due to the alignment logic. Peter
diff --git a/block.c b/block.c index 177720e..74ec342 100644 --- a/block.c +++ b/block.c @@ -2660,28 +2660,53 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs, BlockDriver *drv = bs->drv; QEMUIOVector qiov; struct iovec iov; - int ret; + int ret = 0; - /* TODO Emulate only part of misaligned requests instead of letting block - * drivers return -ENOTSUP and emulate everything */ + /* if no limit is specified in the BlockDriverState use a default + * of 32768 512-byte sectors (16 MiB) per request. + */ + int max_write_zeroes = bs->max_write_zeroes ? bs->max_write_zeroes : 32768; - /* First try the efficient write zeroes operation */ - if (drv->bdrv_co_write_zeroes) { - ret = drv->bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags); - if (ret != -ENOTSUP) { - return ret; + while (nb_sectors > 0 && !ret) { + int num = nb_sectors; + + /* align request */ + if (bs->write_zeroes_alignment && + num >= bs->write_zeroes_alignment && + sector_num % bs->write_zeroes_alignment) { + if (num > bs->write_zeroes_alignment) { + num = bs->write_zeroes_alignment; + } + num -= sector_num % bs->write_zeroes_alignment; } - } - /* Fall back to bounce buffer if write zeroes is unsupported */ - iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE; - iov.iov_base = qemu_blockalign(bs, iov.iov_len); - memset(iov.iov_base, 0, iov.iov_len); - qemu_iovec_init_external(&qiov, &iov, 1); + /* limit request size */ + if (num > max_write_zeroes) { + num = max_write_zeroes; + } - ret = drv->bdrv_co_writev(bs, sector_num, nb_sectors, &qiov); + ret = -ENOTSUP; + /* First try the efficient write zeroes operation */ + if (drv->bdrv_co_write_zeroes) { + ret = drv->bdrv_co_write_zeroes(bs, sector_num, num, flags); + } + + if (ret == -ENOTSUP) { + /* Fall back to bounce buffer if write zeroes is unsupported */ + iov.iov_len = nb_sectors * BDRV_SECTOR_SIZE; + iov.iov_base = qemu_blockalign(bs, iov.iov_len); + memset(iov.iov_base, 0, iov.iov_len); + qemu_iovec_init_external(&qiov, &iov, 1); + + ret = drv->bdrv_co_writev(bs, sector_num, num, &qiov); + + qemu_vfree(iov.iov_base); + } + + sector_num += num; + nb_sectors -= num; + } - qemu_vfree(iov.iov_base); return ret; }
Signed-off-by: Peter Lieven <pl@kamp.de> --- block.c | 57 +++++++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 41 insertions(+), 16 deletions(-)