Changes between Initial Version and Version 1 of AppMultiThread

Timestamp:

Oct 2, 2007, 8:58:17 AM (18 years ago)

Author:

davea

Comment:

--

AppMultiThread

@@ +1 @@
+= API for multi-thread apps =
+
+The following is a design document, not implemented yet.
+
+== Assumptions ==
+
+A 'multi-thread app' A uses multiple threads, say Nthreads(A).
+The average number of processors used, Ncpus(A), may be less
+(because of I/O or synchronization).
+
+Ideally, on a host with N CPUs, we want
+Ncpus(A), summed over running apps, to be about N.
+If it's less, we're not using CPU time.
+If it's more:
+ * we increase latency without increasing throughput
+ * we use more RAM than needed
+ * higher synchronization overhead
+
+We assume that applications may be able to change Nthreads(A) dynamically
+in response to hints from BOINC.
+Nthreads(A) need not be equal to the hint.
+
+Example: suppose
+ * we have an 80-core CPU
+ * app A can use 1,2,4,8,16,32 threads
+ * app B can use 1,2,4,8,16,32,64 threads
+
+Then we want to have either (16,64) or (32,32) threads most of the time.
+
+== Proposal ==
+
+{{{
+int boinc_target_nthreads();
+void boinc_actual_nthreads(int);
+}}}
+
+An application calls boinc_target_nthreads() periodically,
+at points where it is able to change its number of threads.
+It calls boinc_actual_nthreads() to report its actual number of threads.
+
+Shared-memory messages:
+ * core->app (process control channel): <target_nthreads>
+ * app->core (process control channel): <actual_nthreads>
+
+Client maintains estimates of CPU effiency per job,
+uses this to scale target_nthreads.
+
+A WU can specify "max average nthreads"; this is used
+by the client and scheduler to estimate completion time.
+
+Implementation (enforce_schedule()):
+as we schedule jobs, decrement CPU count by scaled actual_nthreads.
+rr_simulation() needs to be modified too.