Re: [Qemu-devel] [Qemu-block] [PATCH v2 4/6] rbd: Switch to byte-based callbacks

[Eric Blake]

On 04/24/2018 02:25 PM, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Make the change for the last few sector-based callbacks
> in the rbd driver.
> 
> Note that the driver was already using byte-based calls for
> performing actual I/O, so this just gets rid of a round trip
> of scaling; however, as I don't know if RBD is tolerant of
> non-sector AIO operations, I went with the conservate approach

s/conservate/conservative/

> of adding .bdrv_refresh_limits to override the block layer
> defaults back to the pre-patch value of 512.
> 
> Signed-off-by: Eric Blake 
> 
-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.   +1-919-301-3266
Virtualization:  qemu.org | libvirt.org




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Re: [Qemu-devel] [Qemu-block] [PATCH v2 4/6] rbd: Switch to byte-based callbacks

[Kevin Wolf]

Am 24.04.2018 um 21:53 hat Jason Dillaman geschrieben:
> On Tue, Apr 24, 2018 at 3:25 PM, Eric Blake  wrote:
> > We are gradually moving away from sector-based interfaces, towards
> > byte-based.  Make the change for the last few sector-based callbacks
> > in the rbd driver.
> >
> > Note that the driver was already using byte-based calls for
> > performing actual I/O, so this just gets rid of a round trip
> > of scaling; however, as I don't know if RBD is tolerant of
> > non-sector AIO operations, I went with the conservate approach
> > of adding .bdrv_refresh_limits to override the block layer
> > defaults back to the pre-patch value of 512.
> >
> > Signed-off-by: Eric Blake 
> >
> > ---
> > v2: override new block layer default alignment [Kevin]
> > ---
> >  block/rbd.c | 44 
> >  1 file changed, 24 insertions(+), 20 deletions(-)
> >
> > diff --git a/block/rbd.c b/block/rbd.c
> > index c9359d0ad84..638ecf8d986 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> > @@ -231,6 +231,13 @@ done:
> >  }
> >
> >
> > +static void qemu_rbd_refresh_limits(BlockDriverState *bs, Error **errp)
> > +{
> > +/* XXX Does RBD support AIO on less than 512-byte alignment? */
> 
> Yes, librbd internally supports 1-byte alignment for IO, but the
> optimal alignment/length would be object size * stripe count.

Would you like to post a follow-up patch to this series that removes the
.bdrv_refresh_limits implementation again with a commit message
explaining that RBD does support byte alignment?

Kevin

Re: [Qemu-devel] [Qemu-block] [PATCH v2 4/6] rbd: Switch to byte-based callbacks

[Jason Dillaman]

On Tue, Apr 24, 2018 at 3:25 PM, Eric Blake  wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Make the change for the last few sector-based callbacks
> in the rbd driver.
>
> Note that the driver was already using byte-based calls for
> performing actual I/O, so this just gets rid of a round trip
> of scaling; however, as I don't know if RBD is tolerant of
> non-sector AIO operations, I went with the conservate approach
> of adding .bdrv_refresh_limits to override the block layer
> defaults back to the pre-patch value of 512.
>
> Signed-off-by: Eric Blake 
>
> ---
> v2: override new block layer default alignment [Kevin]
> ---
>  block/rbd.c | 44 
>  1 file changed, 24 insertions(+), 20 deletions(-)
>
> diff --git a/block/rbd.c b/block/rbd.c
> index c9359d0ad84..638ecf8d986 100644
> --- a/block/rbd.c
> +++ b/block/rbd.c
> @@ -231,6 +231,13 @@ done:
>  }
>
>
> +static void qemu_rbd_refresh_limits(BlockDriverState *bs, Error **errp)
> +{
> +/* XXX Does RBD support AIO on less than 512-byte alignment? */

Yes, librbd internally supports 1-byte alignment for IO, but the
optimal alignment/length would be object size * stripe count.

> +bs->bl.request_alignment = 512;
> +}
> +
> +
>  static int qemu_rbd_set_auth(rados_t cluster, const char *secretid,
>   Error **errp)
>  {
> @@ -899,27 +906,23 @@ failed:
>  return NULL;
>  }
>
> -static BlockAIOCB *qemu_rbd_aio_readv(BlockDriverState *bs,
> -  int64_t sector_num,
> -  QEMUIOVector *qiov,
> -  int nb_sectors,
> -  BlockCompletionFunc *cb,
> -  void *opaque)
> -{
> -return rbd_start_aio(bs, sector_num << BDRV_SECTOR_BITS, qiov,
> - (int64_t) nb_sectors << BDRV_SECTOR_BITS, cb, 
> opaque,
> - RBD_AIO_READ);
> -}
> -
> -static BlockAIOCB *qemu_rbd_aio_writev(BlockDriverState *bs,
> -   int64_t sector_num,
> -   QEMUIOVector *qiov,
> -   int nb_sectors,
> +static BlockAIOCB *qemu_rbd_aio_preadv(BlockDriverState *bs,
> +   uint64_t offset, uint64_t bytes,
> +   QEMUIOVector *qiov, int flags,
> BlockCompletionFunc *cb,
> void *opaque)
>  {
> -return rbd_start_aio(bs, sector_num << BDRV_SECTOR_BITS, qiov,
> - (int64_t) nb_sectors << BDRV_SECTOR_BITS, cb, 
> opaque,
> +return rbd_start_aio(bs, offset, qiov, bytes, cb, opaque,
> + RBD_AIO_READ);
> +}
> +
> +static BlockAIOCB *qemu_rbd_aio_pwritev(BlockDriverState *bs,
> +uint64_t offset, uint64_t bytes,
> +QEMUIOVector *qiov, int flags,
> +BlockCompletionFunc *cb,
> +void *opaque)
> +{
> +return rbd_start_aio(bs, offset, qiov, bytes, cb, opaque,
>   RBD_AIO_WRITE);
>  }
>
> @@ -1158,6 +1161,7 @@ static BlockDriver bdrv_rbd = {
>  .format_name= "rbd",
>  .instance_size  = sizeof(BDRVRBDState),
>  .bdrv_parse_filename= qemu_rbd_parse_filename,
> +.bdrv_refresh_limits= qemu_rbd_refresh_limits,
>  .bdrv_file_open = qemu_rbd_open,
>  .bdrv_close = qemu_rbd_close,
>  .bdrv_reopen_prepare= qemu_rbd_reopen_prepare,
> @@ -1170,8 +1174,8 @@ static BlockDriver bdrv_rbd = {
>  .bdrv_truncate  = qemu_rbd_truncate,
>  .protocol_name  = "rbd",
>
> -.bdrv_aio_readv = qemu_rbd_aio_readv,
> -.bdrv_aio_writev= qemu_rbd_aio_writev,
> +.bdrv_aio_preadv= qemu_rbd_aio_preadv,
> +.bdrv_aio_pwritev   = qemu_rbd_aio_pwritev,
>
>  #ifdef LIBRBD_SUPPORTS_AIO_FLUSH
>  .bdrv_aio_flush = qemu_rbd_aio_flush,
> --
> 2.14.3
>
>



-- 
Jason