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From: | Peter Lieven |
Subject: | Re: [Qemu-devel] [PATCH 1.8 5/6] qemu-img: add option to align writes to cluster_sectors during convert |
Date: | Mon, 25 Nov 2013 16:55:39 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 |
On 25.11.2013 16:50, Paolo Bonzini wrote:
Il 25/11/2013 16:32, Peter Lieven ha scritto:Also, a couple of ideas for separate patches. Perhaps the default value of "-S" could be cluster_size if specified? This would avoid making raw images too fragmented, and compounding filesystem-level fragmentation with qcow2-level fragmentation. And 4K is too small a default in my opinion; it could be easily changed to 64K, though 4K was of course an improvement compared to 512 before commit a22f123 (qemu-img: Require larger zero areas for sparse handling, 2011-08-26).I would vote for 64K or 256K, we already use the first for some time. However, it turned out that (much) bigger values decrease performance. Setting it to cluster_size can be dangerous. As described in my case its 15MB and I think for vhd its 1MB. This can be a lot of zeros that have to be written.What about max(4096, min(bdi->cluster_size, 1048576))?
chaning sparse_size from 65536 to 1048576 about 5% performance decrease... address@hidden:~/git/qemu$ time ./qemu-img convert -pp -m 15728640 -S 1048576 /tmp/VC-Ubuntu-LTS-12.04.2-64bit.qcow2 iscsi://172.21.200.45/iqn.2001-05.com.equallogic:0-8a0906-9d95c510a-344001d54795289f-2012-r2-1-7-0/0 40980480 of 40980480 sectors converted. real 0m29.263s user 0m7.544s sys 0m1.636s address@hidden:~/git/qemu$ time ./qemu-img convert -pp -m 15728640 -S 4096 /tmp/VC-Ubuntu-LTS-12.04.2-64bit.qcow2 iscsi://172.21.200.45/iqn.2001-05.com.equallogic:0-8a0906-9d95c510a-344001d54795289f-2012-r2-1-7-0/0 40980480 of 40980480 sectors converted. real 0m28.169s user 0m7.792s sys 0m1.516s address@hidden:~/git/qemu$ time ./qemu-img convert -pp -m 15728640 -S 65536 /tmp/VC-Ubuntu-LTS-12.04.2-64bit.qcow2 iscsi://172.21.200.45/iqn.2001-05.com.equallogic:0-8a0906-9d95c510a-344001d54795289f-2012-r2-1-7-0/0 40980480 of 40980480 sectors converted. real 0m27.643s user 0m7.644s sys 0m1.520s i wouldn't go over 64k until we fully understand which impact it has. Peter
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