What is below is a useful script to print actionable information from garbage collection logs. As shown by the CMS output below, this is built for the CMS collector. Anything with initial-mark or remark in the output is a “stop the world” operation. You can take the seconds in the last column to determine how often your application was stopped performing these operations for a tenured collection.
-bash-4.1$ awk '$0 ~ "CMS" {i=1;while(++i <= NF) {if ($i ~ "CMS") {gsub("\\[","",$i);component=$i} else if ($i ~ "real=") {split($i,t,"=");gsub(":","",$1);printf("%-40s %-8.2f %-8.2f %-8.2f\n",component,$1-t[2],$1,t[2])}}}' gc.log
CMS-initial-mark: 1115.69 1116.06 0.37
CMS-concurrent-mark: 1116.44 1162.68 46.24
CMS-concurrent-preclean: 1162.68 1171.75 9.07
CMS-concurrent-abortable-preclean: 1171.75 1171.94 0.19
CMS-remark: 1172.15 1172.50 0.35
CMS-concurrent-sweep: 1172.85 1206.67 33.82
CMS-concurrent-reset: 1206.67 1206.71 0.04
CMS-initial-mark: 1990.37 1990.89 0.53
CMS-concurrent-mark: 1991.44 2052.91 61.47
CMS-concurrent-preclean: 2052.91 2056.52 3.61
CMS-concurrent-abortable-preclean: 2056.52 2059.38 2.86
CMS-remark: 2058.34 2059.38 1.04
CMS-concurrent-sweep: 2060.43 2161.88 101.45
CMS-concurrent-reset: 2162.57 2163.41 0.84
CMS-initial-mark: 2301.79 2302.06 0.27
CMS-concurrent-mark: 2302.35 2394.26 91.91
CMS-concurrent-preclean: 2394.26 2415.15 20.89
CMS-concurrent-abortable-preclean: 2415.15 2418.56 3.41
CMS-remark: 2418.13 2418.56 0.43
CMS-concurrent-sweep: 2419.01 2519.19 100.18
CMS-concurrent-reset: 2519.19 2519.21 0.02
CMS-initial-mark: 2559.49 2559.67 0.18
CMS-concurrent-mark: 2559.86 2656.81 96.95
CMS-concurrent-preclean: 2656.82 2675.72 18.90
CMS-concurrent-abortable-preclean: 2675.72 2678.90 3.18
CMS-remark: 2678.00 2678.90 0.90
CMS-concurrent-sweep: 2679.82 2763.69 83.87
CMS-concurrent-reset: 2763.68 2763.72 0.04
CMS-initial-mark: 3062.84 3062.99 0.15
CMS-concurrent-mark: 3063.15 3166.53 103.38
CMS-concurrent-preclean: 3166.56 3203.33 36.77
CMS-remark: 3202.78 3203.34 0.56
CMS-concurrent-sweep: 3203.92 3305.79 101.87
CMS-concurrent-reset: 3305.78 3306.19 0.41
CMS-initial-mark: 3307.88 3308.08 0.20
-bash-4.1$