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Re: [Qemu-devel] [PATCH 10/12] block: Drain throttling queue with BdrvCh
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 10/12] block: Drain throttling queue with BdrvChild callback |
Date: |
Thu, 24 Mar 2016 10:32:33 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
On 24/03/2016 09:25, Kevin Wolf wrote:
> I think your cancellation series (allows to) gets rid of most if not all
> blk_drain() callers in the device emulation, so it becomes harder for
> guests to trigger one. Ideally only the monitor should allow triggering
> a drain.
More precesely you still need to call drain, but indeed they won't be
able to game throttling.
> On the other hand, your other series introduces bdrv_drain() calls where
> we have open-coded nested event loops waiting for a single request
> today. I'm pretty sure that these can be triggered by the guest and that
> throttling the drain would be desirable therefore.
The open-coded nested event loops are typically triggered only from
qemu-io, bdrv_create, etc. They shouldn't be worse than the "disable
throttling for sync I/O" that we used to have.
> Okay. Actually, such a pair of callbacks - not only into the
> BlockBackend, but from there into the guest device - was a thought
> already when we introduced aio_disable_external(). Do you think it would
> make sense to change things in the mid term so that the users of a
> BlockBackend just get drain_begin/end callbacks?
Yes, aio_disable_external and aio_disable_internal can be moved to the
BdrvChildRole callbacks too.
Paolo
- Re: [Qemu-devel] [PATCH 03/12] block: Introduce BlockBackendPublic, (continued)
[Qemu-devel] [PATCH 04/12] block: throttle-groups: Use BlockBackend pointers internally, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 08/12] block: Move I/O throttling configuration functions to BlockBackend, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 11/12] block: Decouple throttling from BlockDriverState, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 05/12] block: Convert throttle_group_get_name() to BlockBackend, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 07/12] block: Move actual I/O throttling to BlockBackend, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 10/12] block: Drain throttling queue with BdrvChild callback, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 06/12] block: Move throttling fields from BDS to BB, Kevin Wolf, 2016/03/22
[Qemu-devel] [PATCH 12/12] block: Don't check throttled reqs in bdrv_requests_pending(), Kevin Wolf, 2016/03/22
Re: [Qemu-devel] [PATCH 00/12] block: Move I/O throttling to BlockBackend, Paolo Bonzini, 2016/03/22