- client: change the calculation of exponential backoff used for

1) individual file transfers
    2) project-level file transfer backoff
    3) scheduler operations
    Old: scale by e.
        Use random backoff in the range min..x
    New: scale by 2.
        Use random backoff in the rand x/2..x
- client: for file transfers, use backoff range of 10 min .. 12 hrs
    rather than 1 min .. 4 hrs


svn path=/trunk/boinc/; revision=21887

checkin_notes

@@ -4991,3 +4991,20 @@ Charlie 9 Jul 2010
         ProjectListCtrl.cpp, .h
         mac/
             MacAccessiblity.cpp
+
+David  9 Jul 2010
+    - client: change the calculation of exponential backoff used for 
+        1) individual file transfers
+        2) project-level file transfer backoff
+        3) scheduler operations
+        Old: scale by e.
+            Use random backoff in the range min..x
+        New: scale by 2.
+            Use random backoff in the rand x/2..x
+    - client: for file transfers, use backoff range of 10 min .. 12 hrs
+        rather than 1 min .. 4 hrs
+
+    client/
+        client_state.cpp,h
+        work_fetch.cpp
+        pers_file_xfer.h

client/client_state.cpp

@@ -1747,20 +1747,15 @@ int CLIENT_STATE::quit_activities() {
     return 0;
 }
 
-// return a random double in the range [rmin,rmax)
-static inline double rand_range(double rmin, double rmax) {
-    if (rmin < rmax) {
-        return drand() * (rmax-rmin) + rmin;
-    } else {
-        return rmin;
-    }
-}
-
-// return a random double in the range [MIN,min(e^n,MAX))
+// Sometime has failed N times.
+// Calculate an exponential backoff between MIN and MAX
 //
-double calculate_exponential_backoff( int n, double MIN, double MAX) {
-    double rmax = std::min(MAX, exp((double)n));
-    return rand_range(MIN, rmax);
+double calculate_exponential_backoff(int n, double MIN, double MAX) {
+    double x = pow(2, (double)n);
+    x *= MIN;
+    if (x > MAX) x = MAX;
+    x *= (.5 + .5*drand());
+    return x;
 }
 
 // See if a timestamp in the client state file

client/client_state.h

@@ -488,25 +488,15 @@ extern double calculate_exponential_backoff(
 
 extern void print_suspend_tasks_message(int);
 
+//////// TIME-RELATED CONSTANTS ////////////
+
+//////// CLIENT INTERNAL
+
 #define POLL_INTERVAL   1.0
     // the client will handle I/O (including GUI RPCs)
     // for up to POLL_INTERVAL seconds before calling poll_slow_events()
     // to call the polling functions
 
-#define CPU_PESSIMISM_FACTOR 0.9
-    // assume actual CPU utilization will be this multiple
-    // of what we've actually measured recently
-
-#define WORK_FETCH_PERIOD   60
-    // see if we need to fetch work at least this often
-
-#define CPU_SCHED_ENFORCE_PERIOD    60
-    // enforce CPU schedule at least this often
-
-#define DEBT_ADJUST_PERIOD CPU_SCHED_ENFORCE_PERIOD
-    // debt is adjusted at least this often,
-    // since adjust_debts() is called from enforce_schedule()
-
 #define GARBAGE_COLLECT_PERIOD  10
     // how often to garbage collect
 
@@ -527,6 +517,30 @@ extern void print_suspend_tasks_message(int);
 
 #define GUI_HTTP_POLL_PERIOD    1.0
 
+//////// WORK FETCH
+
+#define WORK_FETCH_PERIOD   60
+    // see if we need to fetch work at least this often
+#define WF_MIN_BACKOFF_INTERVAL    60
+#define WF_MAX_BACKOFF_INTERVAL    86400
+    // if we ask a project for work for a resource and don't get it,
+    // we do exponential backoff.
+    // This constant is an upper bound for this.
+    // E.g., if we need GPU work, we'll end up asking once a day,
+    // so if the project develops a GPU app,
+    // we'll find out about it within a day.
+
+//////// CPU SCHEDULING
+
+#define CPU_SCHED_ENFORCE_PERIOD    60
+    // enforce CPU schedule at least this often
+
+#define DEBT_ADJUST_PERIOD CPU_SCHED_ENFORCE_PERIOD
+    // debt is adjusted at least this often,
+    // since adjust_debts() is called from enforce_schedule()
+
+//////// NETWORK
+
 #define CONNECT_ERROR_PERIOD    600.0
 
 #define ALLOW_NETWORK_IF_RECENT_RPC_PERIOD  300
@@ -534,6 +548,8 @@ extern void print_suspend_tasks_message(int);
     // that requires network access (e.g. attach to project)
     // allow it even if setting is "no access"
 
+//////// MISC
+
 #define DAILY_XFER_HISTORY_PERIOD   60
 
 #define MAX_STD   (86400)

client/pers_file_xfer.h

@@ -21,9 +21,11 @@
 #include "client_types.h"
 #include "file_xfer.h"
 
-// Default values for exponential backoff
-#define PERS_RETRY_DELAY_MIN    60                // 1 minute
-#define PERS_RETRY_DELAY_MAX    (60*60*4)         // 4 hours
+// min and max for exponential backoff
+// these are multiplied by a random factor .5 .. 1
+//
+#define PERS_RETRY_DELAY_MIN    600
+#define PERS_RETRY_DELAY_MAX    (3600*12)
 #define PERS_GIVEUP             (SECONDS_PER_DAY*90)
     // give up on xfer if this time elapses since last byte xferred
 

client/work_fetch.cpp

@@ -38,15 +38,6 @@ RSC_WORK_FETCH ati_work_fetch;
 RSC_WORK_FETCH cpu_work_fetch;
 WORK_FETCH work_fetch;
 
-#define MIN_BACKOFF_INTERVAL    60
-#define MAX_BACKOFF_INTERVAL    86400
-    // if we ask a project for work for a resource and don't get it,
-    // we do exponential backoff.
-    // This constant is an upper bound for this.
-    // E.g., if we need GPU work, we'll end up asking once a day,
-    // so if the project develops a GPU app,
-    // we'll find out about it within a day.
-
 #define FETCH_IF_IDLE_INSTANCE          0
     // If resource has an idle instance,
     // get work for it from the project with greatest LTD,
@@ -188,7 +179,7 @@ bool RSC_PROJECT_WORK_FETCH::debt_eligible(PROJECT* p, RSC_WORK_FETCH& rwf) {
     // but it's been a while since we asked.
     // In this case, accumulate debt until we reach (around) zero, then stop.
     //
-    if (backoff_interval == MAX_BACKOFF_INTERVAL) {
+    if (backoff_interval == WF_MAX_BACKOFF_INTERVAL) {
         if (long_term_debt > -DEBT_ADJUST_PERIOD) {
             return false;
         }
@@ -200,9 +191,9 @@ bool RSC_PROJECT_WORK_FETCH::debt_eligible(PROJECT* p, RSC_WORK_FETCH& rwf) {
 void RSC_PROJECT_WORK_FETCH::backoff(PROJECT* p, const char* name) {
     if (backoff_interval) {
         backoff_interval *= 2;
-        if (backoff_interval > MAX_BACKOFF_INTERVAL) backoff_interval = MAX_BACKOFF_INTERVAL;
+        if (backoff_interval > WF_MAX_BACKOFF_INTERVAL) backoff_interval = WF_MAX_BACKOFF_INTERVAL;
     } else {
-        backoff_interval = MIN_BACKOFF_INTERVAL;
+        backoff_interval = WF_MIN_BACKOFF_INTERVAL;
     }
     double x = drand()*backoff_interval;
     backoff_time = gstate.now + x;