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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: |
Wed, 23 Mar 2016 22:29:03 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
On 22/03/2016 16:33, Kevin Wolf wrote:
> This removes the last part of I/O throttling from block/io.c and moves
> it to the BlockBackend.
>
> When draining the queue of a BlockDriverState, we must make sure that no
> new requests can come in for it. Request sources from outside the block
> layer are disabled with aio_disable_external(), but the throttling queue
> must be handled separately.
I have looked at the strategy we talked about today to implement request
cancellation (so that e.g. system reset doesn't take ages because of
throttled requests). While that may be a worthwhile addition anyway, I
think throttling bdrv_drain() may impose an excessive cost for cases
such as live migration. The risk of the guest using bdrv_drain() to
game throttling is low enough that we can keep on disabling throttling
during bdrv_drain().
So for now I think we can merge the two series just fine. The strategy
I used in my patch, adding bdrv_no_throttling_begin and
bdrv_no_throttling_end around the bdrv_drain loop, can be adapted just
as use BdrvChildRole callbacks ->drained_begin and ->drained_end.
I will post v3 of my series tomorrow, adopting your patch 1/12 of this
series and removing the recursion on bdrv_no_throttling_begin and
bdrv_no_throttling_end, which is unnecessary.
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
- Re: [Qemu-devel] [PATCH 10/12] block: Drain throttling queue with BdrvChild callback,
Paolo Bonzini <=
[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