trace-cmd: Optimize how pid filters are expressed

Express pid filters as allowed/disallowed filter ranges

  (pid>=100&&pid<=103)

instead of specifying them per pid

  (pid==100||pid==101||pid==102||pid==103)

This makes the size of the resulting filter smaller (and faster) and avoids
overflowing the filter size limit of one page which we can hit on bigger
machines (say >160 CPUs).

Link: http://lore.kernel.org/linux-trace-devel/20190417130959.10064-2-kaslevs@vmware.com

Reported-by: Phil Auld <pauld@redhat.com>
Tested-by: Phil Auld <pauld@redhat.com>
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Slavomir Kaslev <kaslevs@vmware.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 81 insertions, 36 deletions

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 76ca92dc..d5c66ab0 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -950,10 +950,63 @@ static void update_ftrace_pids(int reset)
 static void update_event_filters(struct buffer_instance *instance);
 static void update_pid_event_filters(struct buffer_instance *instance);
 
+static void append_filter_pid_range(char **filter, int *curr_len,
+				    const char *field,
+				    int start_pid, int end_pid, bool exclude)
+{
+	const char *op = "", *op1, *op2, *op3;
+	int len;
+
+	if (*filter && **filter)
+		op = exclude ? "&&" : "||";
+
+	/* Handle thus case explicitly so that we get `pid==3` instead of
+	 * `pid>=3&&pid<=3` for singleton ranges
+	 */
+	if (start_pid == end_pid) {
+#define FMT	"%s(%s%s%d)"
+		len = snprintf(NULL, 0, FMT, op,
+			       field, exclude ? "!=" : "==", start_pid);
+		*filter = realloc(*filter, *curr_len + len + 1);
+		if (!*filter)
+			die("realloc");
+
+		len = snprintf(*filter + *curr_len, len + 1, FMT, op,
+			       field, exclude ? "!=" : "==", start_pid);
+		*curr_len += len;
+
+		return;
+#undef FMT
+	}
+
+	if (exclude) {
+		op1 = "<";
+		op2 = "||";
+		op3 = ">";
+	} else {
+		op1 = ">=";
+		op2 = "&&";
+		op3 = "<=";
+	}
+
+#define FMT	"%s(%s%s%d%s%s%s%d)"
+	len = snprintf(NULL, 0, FMT, op,
+		       field, op1, start_pid, op2,
+		       field, op3, end_pid);
+	*filter = realloc(*filter, *curr_len + len + 1);
+	if (!*filter)
+		die("realloc");
+
+	len = snprintf(*filter + *curr_len, len + 1, FMT, op,
+		       field, op1, start_pid, op2,
+		       field, op3, end_pid);
+	*curr_len += len;
+}
+
 /**
  * make_pid_filter - create a filter string to all pids against @field
  * @curr_filter: Append to a previous filter (may realloc). Can be NULL
- * @field: The fild to compare the pids against
+ * @field: The field to compare the pids against
  *
  * Creates a new string or appends to an existing one if @curr_filter
  * is not NULL. The new string will contain a filter with all pids
@@ -963,54 +1016,46 @@ static void update_pid_event_filters(struct buffer_instance *instance);
  */
 static char *make_pid_filter(char *curr_filter, const char *field)
 {
+	int start_pid = -1, last_pid = -1;
+	int last_exclude = -1;
 	struct filter_pids *p;
-	char *filter;
-	char *orit;
-	char *match;
-	char *str;
+	char *filter = NULL;
 	int curr_len = 0;
-	int len;
 
 	/* Use the new method if possible */
 	if (have_set_event_pid)
 		return NULL;
 
-	len = len_filter_pids + (strlen(field) + strlen("(==)||")) * nr_filter_pids;
-
-	if (curr_filter) {
-		curr_len = strlen(curr_filter);
-		filter = realloc(curr_filter, curr_len + len + strlen("(&&())"));
-		if (!filter)
-			die("realloc");
-		memmove(filter+1, curr_filter, curr_len);
-		filter[0] = '(';
-		strcat(filter, ")&&(");
-		curr_len = strlen(filter);
-	} else
-		filter = malloc(len);
-	if (!filter)
-		die("Failed to allocate pid filter");
-
-	/* Last '||' that is not used will cover the \0 */
-	str = filter + curr_len;
+	if (!filter_pids)
+		return curr_filter;
 
 	for (p = filter_pids; p; p = p->next) {
-		if (p->exclude) {
-			match = "!=";
-			orit = "&&";
-		} else {
-			match = "==";
-			orit = "||";
+		/*
+		 * PIDs are inserted in `filter_pids` from the front and that's
+		 * why we expect them in descending order here.
+		 */
+		if (p->pid == last_pid - 1 && p->exclude == last_exclude) {
+			last_pid = p->pid;
+			continue;
 		}
-		if (p == filter_pids)
-			orit = "";
 
-		len = sprintf(str, "%s(%s%s%d)", orit, field, match, p->pid);
-		str += len;
+		if (start_pid != -1)
+			append_filter_pid_range(&filter, &curr_len, field,
+						last_pid, start_pid,
+						last_exclude);
+
+		start_pid = last_pid = p->pid;
+		last_exclude = p->exclude;
+
 	}
+	append_filter_pid_range(&filter, &curr_len, field,
+				last_pid, start_pid, last_exclude);
 
-	if (curr_len)
-		sprintf(str, ")");
+	if (curr_filter) {
+		char *save = filter;
+		asprintf(&filter, "(%s)&&(%s)", curr_filter, filter);
+		free(save);
+	}
 
 	return filter;
 }