Comment 8 for bug 1290337

@Joseph, thanks for the info and i could install v3.14-rc7-trusty (although i had to switch from nvidia to integrated graphics as nvidia didn't seem to work anymore).

The experience is somewhat mixed so far. In the half-day i'm running it i haven't seen really bad behaviour (no multi-minute apt-get updates) but machine still feels more sluggish than it seems to be when running with old kernel and reduced memory.

And there certainly seems to be still some anomalies: After booting, logging in X and letting the machine's I/O system settle down to idle (according to htop and iotop) i run repeatedly the following command on the otherwise idle machine:

   dd if=/dev/zero of=/tmp/disk-test bs=1M count=1k

As you can see ...

   1073741824 bytes (1.1 GB) copied, 13.5484 s, 79.3 MB/s
   1073741824 bytes (1.1 GB) copied, 14.7879 s, 72.6 MB/s
   1073741824 bytes (1.1 GB) copied, 16.2955 s, 65.9 MB/s
   1073741824 bytes (1.1 GB) copied, 17.5495 s, 61.2 MB/s
   1073741824 bytes (1.1 GB) copied, 19.267 s, 55.7 MB/s
   1073741824 bytes (1.1 GB) copied, 18.9594 s, 56.6 MB/s
   1073741824 bytes (1.1 GB) copied, 19.6092 s, 54.8 MB/s
   1073741824 bytes (1.1 GB) copied, 20.5099 s, 52.4 MB/s
   1073741824 bytes (1.1 GB) copied, 22.3197 s, 48.1 MB/s
   1073741824 bytes (1.1 GB) copied, 20.8351 s, 51.5 MB/s
   1073741824 bytes (1.1 GB) copied, 27.6185 s, 38.9 MB/s
   1073741824 bytes (1.1 GB) copied, 39.5405 s, 27.2 MB/s
   1073741824 bytes (1.1 GB) copied, 55.6986 s, 19.3 MB/s
   1073741824 bytes (1.1 GB) copied, 74.4439 s, 14.4 MB/s
   1073741824 bytes (1.1 GB) copied, 117.431 s, 9.1 MB/s
   1073741824 bytes (1.1 GB) copied, 142.33 s, 7.5 MB/s

... the performance got worse and worse. Looking at `iostat -zmx 3' I/O utilization went down to less than 10% in the last iterations.

However, as soon as i run a single

  /sbin/sysctl -w vm.drop_caches=2

the dd went up again to 90 MB/s!!

So i would be tempted to add the 'kernel-bug-exists-upstream' tag. Thoughts?