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Re: [Qemu-block] blockdev-add I/O throttling parameters

From: Kevin Wolf
Subject: Re: [Qemu-block] blockdev-add I/O throttling parameters
Date: Mon, 20 Feb 2017 16:45:54 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Am 20.02.2017 um 16:30 hat Stefan Hajnoczi geschrieben:
> I/O throttling parameters are missing from blockdev-add.  Is this
> intentional?
> I can imagine two solutions that do not need these parameters in
> blockdev-add:
> 1. I/O throttling is implemented by a BlockDriver.  Users are expected
>    to create the BDS themselves.  This is a little awkward since
>    query-block *does* include the throttling parameters in its output
>    and we must preserve this behavior for existing users.
> 2. block_set_io_throttle must be used after blockdev-add.  Suboptimal
>    because issuing two commands is not atomic (use transaction?).
> Thoughts?

The existing I/O throttling code is working on BlockBackends, but
blockdev-add creates BlockDriverStates. So it can't possibly add
throttling parameters.

The currently recommended solution block_set_io_throttle. The other
option to control BB level thorttling would be to add qdev properties to
the block devices.

In the long term, I think going with 1. and moving throttling to the
block node level is the much nicer (and more flexible) option.


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