Changes between Version 4 and Version 5 of HomogeneousRedundancy

Timestamp:

Jul 6, 2007, 11:28:11 AM (17 years ago)

Author:

davea

Comment:

--

HomogeneousRedundancy

@@ -11 +11 @@
 == Homogeneous redundancy ==
 
-BOINC provides a feature called '''homogeneous redundancy''' to handle divergent applications. You can enable it for a project by including the line
+BOINC provides a feature called '''homogeneous redundancy''' (HR) to handle divergent applications. You can enable it for a project by including the line
 {{{
 <homogeneous_redundancy>N</homogeneous_redundancy>
 }}}
-in the [ProjectConfigFile config.xml] file.
+in the [ProjectConfigFile config.xml] file, where N is the "HR type" to use (see below).
 
-Alternatively, you can enable it selectively for a single application by setting the `homogeneous_redundancy` field in its database record.
+Alternatively, you can enable it selectively for a single application by setting the `homogeneous_redundancy` field in its database record to the HR type for use with that application.
 
-Homogeneous redundancy (HR) divides hosts into 'numerical equivalence classes': two hosts are in the same class if they return identical results for your applications.  The BOINC scheduler will send results for a given workunit only to hosts in the same class; this lets you use strict equality to compare redundant results.
+Homogeneous redundancy divides hosts into 'numerical equivalence classes': two hosts are in the same class if they return identical results for your applications.
+The BOINC scheduler will send results for a given workunit only to hosts in the same class;
+this lets you use strict equality to compare redundant results.
 
-N specifies the granularity of host classification:
+An "HR type" is a host classification.
+Currently the following HR types are defined:
 
  0:: No homogeneous redundancy (all hosts are numerically equivalent)
@@ -28 +31 @@
 
 The proper classification depends on your application, and how it's compiled (compiler, compiler options, math libraries) on the various platforms.
-WCG reports that the following gcc options (on Linux) cause their apps to produce identical results on all processor types:
+For example, WCG reports that the following gcc options (on Linux) cause their apps to produce identical results on all processor types:
 {{{
 -mieee-fp -O3 -fno-rtti -ffor-scope -DNDEBUG
 }}}
+This allows them to use HR type 2.
+
+You can modify these HR types, or add your own, by editing the file
+'''sched/hr.C'''.
+
+If you use HR, it's important to tell the feeder roughly what fraction
+of hosts belong to each HR class;
+this allows it to allocate space in its shared-memory work array
+in proportion to this fraction.
+This information is passed to the feeder in a file '''hr_info.txt'''
+in your project's root directory.
+You can generate this file by running '''sched/census'''
+(you can run this as a periodic task to track changes
+in your host population).
+
+The BOINC distribution includes a file '''sched/sample_hr_info.txt'''
+containing host-distribution data from a large project.
+You can use this e.g., during the period when your project is starting up
+and doesn't have a lot of hosts yet.