Am 12.01.2023 um 21:28 hat Ilya Dryomov geschrieben:
> On Thu, Dec 9, 2021 at 10:34 AM Or Ozeri <o...@il.ibm.com> wrote:
> >
> > The blk_get_max_hw_transfer API was recently added in 6.1.0.
> > It allows querying an underlying block device its max transfer capability.
> > This commit changes virtio-blk to use this.
> >
> > Signed-off-by: Or Ozeri <o...@il.ibm.com>
> > ---
> > hw/block/virtio-blk.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> > index f139cd7cc9..1ba9a06888 100644
> > --- a/hw/block/virtio-blk.c
> > +++ b/hw/block/virtio-blk.c
> > @@ -458,7 +458,7 @@ static void virtio_blk_submit_multireq(BlockBackend
> > *blk, MultiReqBuffer *mrb)
> > return;
> > }
> >
> > - max_transfer = blk_get_max_transfer(mrb->reqs[0]->dev->blk);
> > + max_transfer = blk_get_max_hw_transfer(mrb->reqs[0]->dev->blk);
> >
> > qsort(mrb->reqs, mrb->num_reqs, sizeof(*mrb->reqs),
> > &multireq_compare);
>
> Hi Or,
>
> Superficially, this makes sense to me.
I'm not sure I understand. This is not a passthrough device (unlike
scsi-generic), so why should we consider the hardware limits rather than
the kernel/other backend limits for read/write requests?
See the documentation of both fields:
/*
* Maximal transfer length in bytes. Need not be power of 2, but
* must be multiple of opt_transfer and bl.request_alignment, or 0
* for no 32-bit limit. For now, anything larger than INT_MAX is
* clamped down.
*/
uint32_t max_transfer;
/*
* Maximal hardware transfer length in bytes. Applies whenever
* transfers to the device bypass the kernel I/O scheduler, for
* example with SG_IO. If larger than max_transfer or if zero,
* blk_get_max_hw_transfer will fall back to max_transfer.
*/
uint64_t max_hw_transfer;
Is the real problem that max_transfer isn't right?
Kevin
