svn commit: r187479 - projects/stress2

[Peter Holm]

Author: pho
Date: Tue Jan 20 19:06:10 2009
New Revision: 187479
URL: http://svn.freebsd.org/changeset/base/187479

Log:
  Added comment about the non-deterministic feature of the test.
  
  Approved by:	kib

Modified:
  projects/stress2/README

Modified: projects/stress2/README
==============================================================================
--- projects/stress2/README	Tue Jan 20 19:01:59 2009	(r187478)
+++ projects/stress2/README	Tue Jan 20 19:06:10 2009	(r187479)
@@ -37,3 +37,23 @@ The following sub-directories exists:
 
 The name stress2 indicates that this is the second generation of the Kernel Stress Test Suite.
 The first version (stress) was based mostly on scripts.
+
+
+20090120: des@ pointed out it would be nice to be able to set the
+	random seed in order to be able to reproduce errors in time.
+	A test of this show that the occurrence of panics are still
+	non-deterministic even with a fixed seed. The known broken
+	unionfs was used to test this:
+	http://people.freebsd.org/~pho/stress/log/marcus006.txt.
+	First panic occurred after 29 loops and the second after 8
+	with a seed of "123".
+
+	The randomness that is provided by lack of synchronization
+	with timer interrupt, disk block layout and disk access
+	latencies caused by platter and heads speed changes, disk
+	firmware internal operations, and so on are _much_ bigger
+	then the undeterminism caused by the non-repeatable random
+	seed.
+
+	Anyway, I have always view the this issue as only a slight
+	inconvenience.