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Re: [Qemu-block] [PATCH v2 06/22] block: Add "supports_stats" field to B
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From: |
Alberto Garcia |
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Subject: |
Re: [Qemu-block] [PATCH v2 06/22] block: Add "supports_stats" field to BlockStats |
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Date: |
Fri, 16 Oct 2015 11:49:00 +0200 |
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User-agent: |
Notmuch/0.13.2 (http://notmuchmail.org) Emacs/23.2.1 (i486-pc-linux-gnu) |
On Thu 15 Oct 2015 04:58:22 PM CEST, Stefan Hajnoczi wrote:
>> > If I/O accounting isn't being used then all fields will be 0?
>>
>> Yes, but there's no way to tell if that happens because I/O
>> accounting is not supported or because there hasn't been any I/O yet.
>>
>> There's one additional problem: this patch assumes that accounting is
>> supported if this BDS is attached to a BlockBackend. But we don't
>> know if the device model supports accounting or not, I still need to
>> figure out what's the best way to do it.
>
> Is there a corresponding libvirt patch or why does it matter whether
> the QMP client can detect whether blockstats are available?
I'm thinking that keeping this patch as it is now is probably not very
useful.
Block statistics are kept in the BlockBackend, so the only BDS that is
going to have data != 0 when you call query-blockstats is the topmost
one. There's probably no need to have an additional flag for this.
If you disconnect a BlockBackend from a device model that implements
accounting and then connect it to one that does not, there's no way for
the client to know that. That's probably worth exposing in the API, but
this patch does not do that yet, so I think we can skip it for now.
Berto
- [Qemu-block] [PATCH v2 04/22] util: Infrastructure for computing recent averages, (continued)
- [Qemu-block] [PATCH v2 04/22] util: Infrastructure for computing recent averages, Alberto Garcia, 2015/10/08
- [Qemu-block] [PATCH v2 02/22] ide: Account for write operations correctly, Alberto Garcia, 2015/10/08
- [Qemu-block] [PATCH v2 18/22] atapi: Account for failed and invalid operations, Alberto Garcia, 2015/10/08
- [Qemu-block] [PATCH v2 22/22] block: Update copyright of the accounting code, Alberto Garcia, 2015/10/08
- [Qemu-block] [PATCH v2 06/22] block: Add "supports_stats" field to BlockStats, Alberto Garcia, 2015/10/08
[Qemu-block] [PATCH v2 07/22] block: Add statistics for failed and invalid I/O operations, Alberto Garcia, 2015/10/08
[Qemu-block] [PATCH v2 09/22] block: Compute minimum, maximum and average I/O latencies, Alberto Garcia, 2015/10/08
[Qemu-block] [PATCH v2 19/22] ide: Account for failed and invalid operations, Alberto Garcia, 2015/10/08
[Qemu-block] [PATCH v2 21/22] scsi-disk: Account for failed operations, Alberto Garcia, 2015/10/08
[Qemu-block] [PATCH v2 01/22] xen_disk: Account for flush operations, Alberto Garcia, 2015/10/08
[Qemu-block] [PATCH v2 15/22] nvme: Account for failed and invalid operations, Alberto Garcia, 2015/10/08