Re: [Qemu-block] [Qemu-devel] [PATCH for-2.8 0/2] pass partial discard requests all the way down

[Laszlo Ersek]

On 11/11/16 00:10, Eric Blake wrote:
> Peter reported a mild regression in qemu 2.7 when targetting the
> Dell Equallogic iSCSI, which advertizes a preferred and maximum
> unmap alignment at 15M.  In qemu 2.6, trims not aligned to those
> boundaries still made it to the device, but in 2.7, the block
> layer is ignoring unaligned portions of guest requests, resulting
> in fewer blocks being actually trimmed.
> 
> Since discard is advisary,

advisory?

> it is borderline if this counts as a
> bug fix worthy for inclusion in 2.8, or if it should be deferred
> to 2.9.  At any rate, while I was able to test that the patch
> didn't misbehave for me when I tweaked an NBD setup to force
> 15M alignment, I am unable to test that it makes an actual
> difference for Peter's hardware, and that needs to happen before
> anyone even thinks of applying this.
> 
> Eric Blake (2):
>   block: Return -ENOTSUP rather than assert on unaligned discards
>   block: Pass unaligned discard requests to drivers
> 
>  block/io.c       | 36 +++++++++++++++++++++++-------------
>  block/iscsi.c    |  4 +++-
>  block/qcow2.c    |  4 ++++
>  block/sheepdog.c |  5 +++--
>  4 files changed, 33 insertions(+), 16 deletions(-)
>