Re: [Qemu-devel] Throttling groups vs filter nodes

[Alberto Garcia]

On Mon 29 May 2017 10:57:37 PM CEST, Manos Pitsidianakis wrote:
>>> A quirk in the current implementation is that the throttling limits
>>> for the group are overwritten by each -drive throttling.group=group0.
>>> Limits for all but the last -drive in a group are ignored.
>>   - bps or iops != 0   -> set the I/O limits of a throttling group. The
>>                           selected device is moved to that group if it
>>                           wasn't there yet.
>>
>>   - bps and iops == 0  -> remove a device from a throttling group
>>                           without touching that group's I/O limits.
>
> These are very unintuitive. However, even without considering
> backwards compatibility, I think that using -object notation (eg
> "object-add throttle-group,id=foo,iops=...) is intuitive in the case
> of groups, but not when you need individual limits for each device as
> the syntax would be too verbose.  Of course the old interface covers
> that.

Yes, that's clear. I think that when adding drives, the command-line UI
-drive throttling.iops=XXX notation is good enough for individual
devices and the -object notation is good for groups.

My question was about the block_set_io_throttle QMP command, which you
can use to change the limits of existing drives.

But I think Kevin is right and we should probably think of an
alternative interface for that.

Berto