From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Sat, 16 Jun 2012 19:14:03 +0000 (-0400)
Subject: rcuja testpop: print extra items in subclass instead of confusing "unbalance"
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=c7b5bcc325eeb21c655403563b1526814ab05bf3;p=userspace-rcu.git

rcuja testpop: print extra items in subclass instead of confusing "unbalance"

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/rcuja/design.txt b/rcuja/design.txt
index 89e66b9..c126f77 100644
--- a/rcuja/design.txt
+++ b/rcuja/design.txt
@@ -143,16 +143,19 @@ linear arrays).
 Assuming that finding the exact sub-pool usage maximum for any given
 distribution is NP complete (not proven).
 
-Taking into account unbalance ratios (tested programmatically by
+Taking into account sub-class size unbalance (tested programmatically by
 randomly taking N entries from 256, calculating the distribution for
 each bit (number of nodes for which bit is one/zero), and calculating
 the difference in number of nodes for each bit, choosing the minimum
 difference -- for millions of runs).
 
-tot entries   unbalance       largest linear array (stat. approx.)
+We start from the "ideal" population size (with no unbalance), and do a
+fixed point to find the appropriate population size.
+
+tot entries    subclass extra items       largest linear array (stat. approx.)
 ---------------------------------------------------------------------
-48 entries:      2 (98%)              24+1=25 (target ~50/2=25)
-54 entries:      2 (97%)              27+1=28 (target ~56/2=28)
+48 entries:      1 (98%)                  24+1=25 (target ~50/2=25)
+54 entries:      1 (97%)                  27+1=28 (target ~56/2=28)
 
 Note: there exists rare worse cases where the unbalance is larger, but
 it happens _very_ rarely. But need to provide a fallback if the subclass
@@ -162,10 +165,10 @@ does not fit, but it does not need to be efficient.
 For pool of size 4, we need to approximate what is the maximum unbalance
 we can get for choice of distributions grouped by pairs of bits.
 
-tot entries     unbalance     largest linear array (stat. approx.)
+tot entries     subclass extra items   largest linear array (stat. approx.)
 ---------------------------------------------------------------------
-92 entries:      8 (99%)             23+2=25  (target: ~100/4=25)
-104 entries:     8 (99%)             26+2=28  (target: ~112/4=28)
+92 entries:      2 (99%)                23+2=25  (target: ~100/4=25)
+104 entries:     2 (99%)                26+2=28  (target: ~112/4=28)
 
 
 Note: there exists rare worse cases where the unbalance is larger, but
diff --git a/rcuja/testpop.c b/rcuja/testpop.c
index 50d7a21..002ebac 100644
--- a/rcuja/testpop.c
+++ b/rcuja/testpop.c
@@ -21,12 +21,9 @@
  */
 
 /*
- * This program generates random populations, and shows the worse-case
- * unbalance, as well as the distribution of unbalance encountered.
- * Remember that the unbalance is the delta between the lowest and
- * largest population. Therefore, to get the delta between the subclass
- * size and the actual number of items, we need to divide the unbalance
- * by the number of subclasses (by hand).
+ * This program generates random populations, and shows the largest
+ * sub-class generated, as well as the distribution of sub-class size
+ * for the largest sub-class of each population.
  */
 
 #include <stdio.h>
@@ -45,9 +42,9 @@ static uint8_t pool[256];
 static uint8_t nr_one[8];
 static uint8_t nr_2d_11[8][8];
 static uint8_t nr_2d_10[8][8];
-static int global_max_minunbalance = 0;
+static int global_max_minsubclass_len = 0;
 
-static unsigned int unbalance_distrib[256];
+static unsigned int subclass_len_distrib[256];
 
 static
 uint8_t random_char(void)
@@ -147,7 +144,7 @@ void print_count(void)
 static
 void stat_count(void)
 {
-	int minunbalance = INT_MAX;
+	int minsubclass_len = INT_MAX;
 
 	if (nr_distrib == 2) {
 		int i;
@@ -158,8 +155,8 @@ void stat_count(void)
 			diff = (int) nr_one[i] * 2 - sel_pool_len;
 			if (diff < 0)
 				diff = -diff;
-			if (diff < minunbalance) {
-				minunbalance = diff;
+			if ((diff >> 1) < minsubclass_len) {
+				minsubclass_len = diff >> 1;
 			}
 		}
 	}
@@ -181,17 +178,17 @@ void stat_count(void)
 				/* Get max linear array size */
 				if (diff[1] > diff[0])
 					diff[0] = diff[1];
-				if (diff[0] < minunbalance) {
-					minunbalance = diff[0];
+				if ((diff[0] >> 2) < minsubclass_len) {
+					minsubclass_len = diff[0] >> 2;
 				}
 			}
 		}
 	}
 
-	if (minunbalance > global_max_minunbalance) {
-		global_max_minunbalance = minunbalance;
+	if (minsubclass_len > global_max_minsubclass_len) {
+		global_max_minsubclass_len = minsubclass_len;
 	}
-	unbalance_distrib[minunbalance]++;
+	subclass_len_distrib[minsubclass_len]++;
 }
 
 static
@@ -201,15 +198,15 @@ void print_distrib(void)
 	unsigned long long tot = 0;
 
 	for (i = 0; i < 256; i++) {
-		tot += unbalance_distrib[i];
+		tot += subclass_len_distrib[i];
 	}
 	if (tot == 0)
 		return;
 	printf("Distribution:\n");
 	for (i = 0; i < 256; i++) {
 		printf("(%u, %u, %llu%%) ",
-			i, unbalance_distrib[i],
-			100 * (unsigned long long) unbalance_distrib[i] / tot);
+			i, subclass_len_distrib[i],
+			100 * (unsigned long long) subclass_len_distrib[i] / tot);
 	}
 	printf("\n");
 }
@@ -217,8 +214,8 @@ void print_distrib(void)
 static
 void print_stat(uint64_t i)
 {
-	printf("after %llu pools, global_max_minunbalance: %d\n",
-		(unsigned long long) i, global_max_minunbalance);
+	printf("after %llu pools, global_max_minsubclass_len extra: %d\n",
+		(unsigned long long) i, global_max_minsubclass_len);
 	print_distrib();
 }