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Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver |
Date: |
Thu, 21 Feb 2013 16:28:14 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 |
Il 21/02/2013 16:25, Dietmar Maurer ha scritto:
>>> I just posted v5 of the patch. But I get a slow down of 15% if I use
>>> bdrv_is_allocated_above. (tested with empty qcow2 files.)
>>
>> Strange, for an unallocated area bdrv_is_allocated_above and bdrv_read really
>> do the same thing apart from writing the zeroes to the buffer.
>> The code looks okay, does a profile say where the time is being spent?
>> Or does the is_allocated_above ever trigger (are you using metadata
>> preallocation)?
>
> Yes, I use metadata preallocation. But that does not explain why it gets
> slower?
Because then this is not an empty qcow2 file, it is a full qcow2 file
where reads are particularly cheap because they always hit holes. It is
the worst case for this optimization, I think 15% is not wonderful but
not particularly bad.
>> BTW, any reason why BACKUP_BLOCKS_PER_CLUSTER is hardcoded and you're
>> not using the cluster size from bdrv_get_info?
>
> A backup includes several block devices, and I want to have the same cluster
> size
> for all. It makes the code easier.
Paolo
- [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, (continued)
- [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Dietmar Maurer, 2013/02/19
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Eric Blake, 2013/02/19
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Paolo Bonzini, 2013/02/20
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Dietmar Maurer, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Paolo Bonzini, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Dietmar Maurer, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Dietmar Maurer, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Dietmar Maurer, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Paolo Bonzini, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver, Dietmar Maurer, 2013/02/21
- Re: [Qemu-devel] [PATCH v3 2/6] add basic backup support to block driver,
Paolo Bonzini <=
Re: [Qemu-devel] [PATCH v3 1/6] RFC: Efficient VM backup for qemu, Eric Blake, 2013/02/19
Re: [Qemu-devel] [PATCH v3 1/6] RFC: Efficient VM backup for qemu, Dietmar Maurer, 2013/02/20