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Re: [Qemu-block] blockdev-add I/O throttling parameters
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-block] blockdev-add I/O throttling parameters |
Date: |
Tue, 21 Feb 2017 11:17:42 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Mon, Feb 20, 2017 at 05:29:19PM +0100, Alberto Garcia wrote:
> On Mon, Feb 20, 2017 at 04:45:54PM +0100, Kevin Wolf wrote:
> > > 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?).
> >
> > 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.
>
> Yeah I agree with Kevin.
Okay, thanks for clarifying.
Stefan
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