[libvirt] RFC: exposing qemu's block-set-write-threshold

[Eric Blake]

On 05/19/2015 06:42 AM, Eric Blake wrote:

> On the other hand, it might make sense to allow BlockIoTune on backing
> chains - for a difference in throttling between the main image and its
> backing image.  That is, I could possibly see a case where a local image
> is based on top of a network backing file, and where we want to read the
> local image with no throttling, but read the backing file with rate
> limiting in effect to avoid saturating the network; in such a setup, the
> user is likely going to do a blockpull to move data off the network onto
> the local copy, but doesn't want the pull to affect performance.  Or
> conversely, someone could have a setup where the backing file has no
> rate limit, but the active file is rate-limited (and thus the guest
> performs faster the closer it is to the original backing file, as a way
> of measuring how much the guest differs from the golden image).  Of
> course, we're still waiting for per-node throttling to land in qemu:
> https://lists.gnu.org/archive/html/qemu-devel/2015-04/msg01196.html

And _while I was typing_, that got bumped from v7 to v8:
https://lists.gnu.org/archive/html/qemu-devel/2015-05/msg03716.html

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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