[linux-mm-cc] compcache performance data

John Mitchell johnlmitchell at gmail.com
Thu Jun 11 18:34:28 EDT 2009


Hi!  I've recently started working with compcache, and have a few questions
in addition to a little data to contribute.

- what's the "sweet spot" for which compcache is most appropriate?

I've read about using this for netbooks, where CPU is relatively free, it
has limited memory, and disk is at a premium.

- for this sweet spot, what's the best test load, to measure performance?
How can this be made repeatable?

The wiki mentions "load Firefox, OpenOffice, and 3 evince windows", but that
doesn't sound very repeatable.  The "scan" benchmark is very easy to use and
is repeatable, but how comparable is it to real-world information?


For my tests, I ran three configurations of swap: traditional swap to disk,
compcache only, and compcache with disk as backing store.  The plot is
linked below, and I'm happy to publish data & scripts if that is useful.  I
found that using compcache completed the workload quite a bit faster than
just with disk-based swap, and compcache+backing store was faster.

However, I realized that the numbers can be *very* specific to differing
sizes of RAM, compcache, swap disk, and workload.  Nor do I trust that
"swapping is faster" is a concrete metric to optimize.


** How can I tune my system and load to best get results from compcache?
For a VM, how much 1) RAM, 2) swap disk, and 3) how much compcache
allocation?  What's the test load?


Thanks so much!
- john



Testing done under Linux VM (KVM), compcache-0.5.3

- VM details:
  . 128 MiB RAM, swap: ~152 MiB
  . 1 CPU, QEMU 0.9.1
  . Ubuntu 9.04 (kernel 2.6.28-11-generic)
  . disk ~20 MB.sec buffered disk reads ("hdparm -Tt")

- Host details:
  . Intel(R) Core(TM)2 CPU          6600  @ 2.40GHz
  . Ubuntu 9.04 (kernel 2.6.28-11-generic)

Testing details

- full boot, runlevel 5
- run "scan 152 2" (ie allocate 152MiB and scan twice)
- run above test once for: disk based swap, ramzswap, and ramzswap with
backing store


http://www.flickr.com/photos/shavenwarthog/3618101530/
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