Changes between Version 25 and Version 26 of GpuWorkFetch

Timestamp:

Jan 27, 2009, 10:54:31 AM (16 years ago)

Author:

davea

Comment:

--

GpuWorkFetch

@@ -92 +92 @@
 and so on.
 
-*** Question:  If we need to contact a project for a tasks of two different types, and one of the backoffs is satisfied, do we ask for both types?
+Note: if we decide to ask a project for work for resource A,
+we may ask it for resource B as well, even if it's backed off for B.
 
 === Long-term debt ===
 
-We'll continue to use the idea of '''long-term debt''' (LTD),
-which represents how much work (measured in device instance-seconds) is "owed" to each project P.
+We continue to use the idea of '''long-term debt''' (LTD),
+representing how much work (measured in device instance-seconds) is "owed" to each project P.
 This increases over time in proportion to P's resource share,
 and decreases as P uses resources.
-Simplified summary of the new policy: when we need work for a resource,
-we ask the project that may have that type of job and whose LTD is greatest.
-
-The idea of using RAC as a surrogate for LTD was discussed and set aside for various reasons.
+Simplified summary of the new policy: when we need work for a resource R,
+we ask the project that is not backed off for R and whose LTD is greatest.
 
 The notion of LTD needs to span resources;
@@ -121 +120 @@
  * The "overall LTD", which is used in the work-fetch decision, is the sum of the resource LTDs, weighted by the speed of the resource (FLOPs per instance-second).
 
-Next we need to specify exactly how LTD is maintained.
-It's clear how it decreases; the question is, how is it increased?
-We need to avoid situations where LTD increases without bound.
-
-The design is as follows.
-A project P accumulates debt for a resource when:
- * P is not backed off for that resource, and the backoff interval is not at the max.
+Per-resource LTD is maintained as follows:
+
+A project is "debt eligible" for a resource R if:
+
+ * P is not backed off for R, and the backoff interval is not at the max.
  * P is not suspended via GUI, and "no more tasks" is not set
 
-The rate at which P accumulates debt is its resource share relative
-to all the projects satisfying the above.
-
-When an application has used N instances of a resource for a time T,
-its debt decreases by an amount proportional to N*T.
+Debt is adjusted as follows:
+ * For each debt-eligible project P, the debt is increased by the amount it's owed (delta T times its resource share relative to other debt-eligible projects) minus the amount it got (the number of instance-seconds).
+ * An offset is added to debt-eligible projects so that the net change is zero.  This prevents debt-eligible projects from drifting away from other projects.
+ * An offset is added so that the maximum debt across all projects is zero (this ensures that when a new project is attached, it starts out debt-free).
+
 
 === Work-fetch state ===
@@ -298 +295 @@
       seconds_to_fill
 }}}
+
+== Notes ==
+
+The idea of using RAC as a surrogate for LTD was discussed and set aside for various reasons.