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@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@netapp.com www.netapp.com
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