On 8/17/20 7:32 AM, Peter Lieven wrote:
Hi,
I am currently debugging a performance issue in qemu-img convert. I
think I have found the cause and will send a patch later.
But is there any reason why BDRV_REQUEST_MAX_SECTORS is not at least
aligned down to 8 (4k sectors)?
Any operation that is not able to determinate an optimal or maximum
request size from a driver will likely use this value and
might generate unaligned requests (as qemu-img convert does) as soon as
the first iteration of an operation is done.
Vladimir's work to make the block layer 64-bit clean should help resolve
this, as we will be relying more heavily on values aligned to the
driver's limits rather than arbitrary 32-bit cutoffs.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
