Changes between Initial Version and Version 1 of GpuSync

Timestamp:

Nov 5, 2010, 3:11:01 PM (14 years ago)

Author:

davea

Comment:

--

GpuSync

@@ +1 @@
+= Support for synchronous GPU apps =
+
+GPU apps run much faster, like 2X,
+if their CPU and GPU parts synchronize using busy-waiting instead of interrupts.
+(Busy-waiting means it uses 100% of a CPU,
+and this process runs at normal OS scheduling priority.)
+E.g. you might get a 100 GFLOPS increase in GPU speed
+at the expense of 5 GFLOPS of CPU speed.
+
+However, many volunteers do not want this behavior,
+so we can't make it the default.
+
+This raises several issues:
+
+== What is the volunteer interface? ==
+
+Possibilities:
+ * A new preference.
+   Pros: automatically propagated; available to server.
+   Cons: too many prefs already.
+ * Config file flag.
+   Pros: simple.
+   Cons: nor propagated.
+
+I'd lean towards a new pref.
+
+Gianni suggested adding a new "Use GPU Full Speed" item to
+the activity menu, but this isn't practical - among other things,
+it would prevent the use of GPU prefs like
+"don't use GPU when computer is in use".
+
+What are the semantics?
+If the user changes the pref (or config option)
+should running GPU jobs change their synch mode?
+What about unstarted jobs?
+
+== How does it affect apps? ==
+
+Should there be separate app versions for the 2 types of synch?
+No; that would prevent users from changing mode mid-job.
+Apps should be able to do either type of synch, based on a flag in APP_INIT_DATA.
+Let's call such app versions '''synch-selectable'''.
+
+BOINC needs to know whether a given app version is synch-selectable.
+We'll do this with an element in the app version's XML doc
+(update_versions will have to be changed to support this).
+
+== How does it affect server scheduling? ==
+
+What avg_ncpus does the scheduler report?
+
+What avg_ncpus does it use in accounting the CPU seconds for jobs sent?
+
+How is job completion time estimation impacted?
+(potentially not at all - the system will adapt).
+
+== How does it affect client scheduling? ==
+
+Let's assume that app_version.avg_ncpus is the non-busywait value (e.g. 0.1 or so).
+
+If the full-speed pref is set,
+and the app version is synch-selectable,
+then the client needs to set avg_ncpus to 1.
+Otherwise we'll overcommit the CPUs.
+(Note: we need to save the original avg_ncpus somewhere,
+in case the user turns off the pref).