Ubuntu
linux package

  1. Bug #1390354
  2. Comment #4

Comment 4 for bug 1390354

Revision history for this message
Markus Fischer (markus-fischer) wrote :

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.