[libvirt] NFS over RDMA small block DIRECT_IO bug

[Andrew Holway]

> 
> That is expected behaviour. DIRECT_IO over RDMA needs to be page aligned
> so that it can use the more efficient RDMA READ and RDMA WRITE memory
> semantics (instead of the SEND/RECEIVE channel semantics).

Yes, I think I am understanding that now.

I need to find a way of getting around the lib-virt issue.

http://lists.gnu.org/archive/html/qemu-devel/2011-12/msg01570.html

Thanks,

Andrew


> 
>> I want to run my KVM guests on top of NFS over RDMA. My guests cannot create filesystems.
>> 
>> Thanks,
>> 
>> Andrew.
>> 
>> bug report: https://bugzilla.linux-nfs.org/show_bug.cgi?id=228
>> 
>> [root at node001 mnt]# for f in 512 1024 2048 4096 8192 16384 32768 65536 131072; do dd bs="$f" if=CentOS-6.3-x86_64-netinstall.iso of=hello iflag=direct oflag=direct && md5sum hello && rm -f hello; done
>> 
>> 409600+0 records in
>> 409600+0 records out
>> 209715200 bytes (210 MB) copied, 62.3649 s, 3.4 MB/s
>> aadd0ffe3c9dfa35d8354e99ecac9276  hello -- 512 byte block 
>> 
>> 204800+0 records in
>> 204800+0 records out
>> 209715200 bytes (210 MB) copied, 41.3876 s, 5.1 MB/s
>> 336f6da78f93dab591edc18da81f002e  hello -- 1K block
>> 
>> 102400+0 records in
>> 102400+0 records out
>> 209715200 bytes (210 MB) copied, 21.1712 s, 9.9 MB/s
>> f4cefe0a05c9b47ba68effdb17dc95d6  hello -- 2k block
>> 
>> 51200+0 records in
>> 51200+0 records out
>> 209715200 bytes (210 MB) copied, 10.9631 s, 19.1 MB/s
>> 690138908de516b6e5d7d180d085c3f3  hello -- 4k block
>> 
>> 25600+0 records in
>> 25600+0 records out
>> 209715200 bytes (210 MB) copied, 5.4136 s, 38.7 MB/s
>> 690138908de516b6e5d7d180d085c3f3  hello
>> 
>> 12800+0 records in
>> 12800+0 records out
>> 209715200 bytes (210 MB) copied, 3.1448 s, 66.7 MB/s
>> 690138908de516b6e5d7d180d085c3f3  hello
>> 
>> 6400+0 records in
>> 6400+0 records out
>> 209715200 bytes (210 MB) copied, 1.77304 s, 118 MB/s
>> 690138908de516b6e5d7d180d085c3f3  hello
>> 
>> 3200+0 records in
>> 3200+0 records out
>> 209715200 bytes (210 MB) copied, 1.4331 s, 146 MB/s
>> 690138908de516b6e5d7d180d085c3f3  hello
>> 
>> 1600+0 records in
>> 1600+0 records out
>> 209715200 bytes (210 MB) copied, 0.922167 s, 227 MB/s
>> 690138908de516b6e5d7d180d085c3f3  hello
>> 
>> 
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> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer
> 
> NetApp
> Trond.Myklebust at netapp.com
> www.netapp.com
> 
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