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Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alterna
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size |
Date: |
Mon, 25 Nov 2013 16:14:25 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 |
Il 25/11/2013 16:07, Peter Lieven ha scritto:
>>> since the convert process is basically a sync operation it might
>>> be benificial in some case to change the hardcoded I/O buffer
>>> size to an alternate (greater) value.
>> Do you really need the extra knob? You can just add to BlockLimits the
>> optimal transfer length, and use it unconditionally.
> If you say patch 5 and 3 are ok. What could be done is to remove
> this knob and increase the iobuf_size to cluster_size if cluster_size
> is greater.
Yes, that makes sense because it avoids unnecessary COW.
> I do not want to increase the default iobuf size to anything
> greater than 2MB. I do not know why this was choosen, but maybe
> there was a reason for it.
I think it is fine to increase it to the cluster_size or even to the
optimal transfer length (new BlockLimits field).
> The storages we use here have a very strange page size of 15MB.
> If I sent aligned 15MB chunks the performace is about +50% compared
> to the original qemu-img.
I think composing the optimal transfer length and optimal unmap
granularity (cluster_size) will work well:
* clamp maximum size to optimal transfer length
* then, round final sector down to unmap granularity
Paolo
- [Qemu-devel] [PATCH 1.8 0/6] qemu-img convert optimizations, Peter Lieven, 2013/11/25
- [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Peter Lieven, 2013/11/25
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Paolo Bonzini, 2013/11/25
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Peter Lieven, 2013/11/25
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Peter Lieven, 2013/11/25
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Peter Lieven, 2013/11/25
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Paolo Bonzini, 2013/11/25
- Re: [Qemu-devel] [PATCH 1.8 3/6] qemu-img: add option to specify alternate iobuffer size, Peter Lieven, 2013/11/25
[Qemu-devel] [PATCH 1.8 2/6] qemu-img: fix usage instruction for qemu-img convert, Peter Lieven, 2013/11/25
[Qemu-devel] [PATCH 1.8 1/6] qemu-img: add support for skipping zeroes in input during convert, Peter Lieven, 2013/11/25
[Qemu-devel] [PATCH 1.8 4/6] block/iscsi: set bdi->cluster_size, Peter Lieven, 2013/11/25