I found the problem: The stock Ubuntu Server 14.04.1 amd64 iso image currently downloadable comes with a kernel which has the flag CONFIG_CONTEXT_TRACKING_FORCE=y . Recompiling the kernel without this flag set or upgrading to a kernel without the flag fixes the performance issues:
Multiple CPU, stock 14.04.1 kernel (3.13.0-32): vagrant@ubuntu-14:~$ dd if=/dev/zero of=bigfile bs=1024 count=5000000 5000000+0 records in 5000000+0 records out 5120000000 bytes (5.1 GB) copied, 46.6511 s, 110 MB/s Multiple CPUs, recompiled kernel (3.13.0-39 ; but I tested this specific kernel with both flag enabled/disabled): vagrant@ubuntu-14:~$ dd if=/dev/zero of=bigfile bs=1024 count=5000000 5000000+0 records in 5000000+0 records out 5120000000 bytes (5.1 GB) copied, 10.4548 s, 490 MB/s It seems this specific flag has been brought up in another report ( https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1349028 ) and is already fixed/soon to be released. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1390354 Title: Ubuntu Server 14.04.1 as VirtualBox Guest disk performance drops with more than once CPU To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1390354/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
