From: Frank Ch. Eigler <fche@elastic.org>
Date: Thu, 6 May 2010 17:04:11 +0000 (-0400)
Subject: PR11575: lengthen TRYLOCKDELAY
X-Git-Tag: release-1.3~374
X-Git-Url: https://sourceware.org/git/?a=commitdiff_plain;h=26f62be4d9b2cfc975a07b96b988da2a62c30b71;p=systemtap.git

PR11575: lengthen TRYLOCKDELAY

Change default timeout for global variable locks to apprx. 1 ms,
in 10us chunks.  TRYLOCKDELAY now measures microseconds.

* translate.cxx (translate_pass): Change TRYLOCKDELAY and
  MAXTRYLOCK default values.
* runtime/probe_lock.h (stp_lock_probe): Use udelay() rather than
  ndelay().
* runtime/time.c (STP_TIMELOCK*): New macros just for time seqlock
  timeout purposes.  Expected contention is negligible here.
---

diff --git a/runtime/probe_lock.h b/runtime/probe_lock.h
index 1077f4c60..f1c86f7da 100644
--- a/runtime/probe_lock.h
+++ b/runtime/probe_lock.h
@@ -1,5 +1,5 @@
 /* probe locking header file
- * Copyright (C) 2009 Red Hat Inc.
+ * Copyright (C) 2009-2010 Red Hat Inc.
  *
  * This file is part of systemtap, and is free software.  You can
  * redistribute it and/or modify it under the terms of the GNU General
@@ -48,13 +48,13 @@ stp_lock_probe(const struct stp_probe_lock *locks, unsigned num_locks)
 			while (!write_trylock(locks[i].lock)) {
 				if (++retries > MAXTRYLOCK)
 					goto skip;
-				ndelay (TRYLOCKDELAY);
+				udelay (TRYLOCKDELAY);
 			}
 		else
 			while (!read_trylock(locks[i].lock)) {
 				if (++retries > MAXTRYLOCK)
 					goto skip;
-				ndelay (TRYLOCKDELAY);
+				udelay (TRYLOCKDELAY);
 			}
 	}
 	return 1;
diff --git a/runtime/time.c b/runtime/time.c
index 5caa73cc4..0d13487f3 100644
--- a/runtime/time.c
+++ b/runtime/time.c
@@ -269,6 +269,14 @@ _stp_init_time(void)
     return ret;
 }
 
+
+#ifndef STP_TIMELOCKDELAY
+#define STP_TIMELOCKDELAY 100 /* ns */
+#endif
+#ifndef STP_TIMELOCKTRIES
+#define STP_TIMELOCKTRIES 10 /* total 1 us */
+#endif
+
 static int64_t
 _stp_gettimeofday_ns(void)
 {
@@ -283,17 +291,20 @@ _stp_gettimeofday_ns(void)
     if (!stp_time)
         return -1;
 
-    preempt_disable();
+    preempt_disable(); /* XXX: why?  Isn't this is only run from probe handlers? */
     time = per_cpu_ptr(stp_time, smp_processor_id());
 
     seq = read_seqbegin(&time->lock);
     base = time->base_ns;
     last = time->base_cycles;
     freq = time->freq;
-    while (unlikely(read_seqretry(&time->lock, seq))) {
-        if (unlikely(++i >= MAXTRYLOCK))
-            return 0;
-        ndelay(TRYLOCKDELAY);
+    while (unlikely(read_seqretry(&time->lock, seq))) { 
+            if (/* very */ unlikely(++i >= STP_TIMELOCKTRIES)) {
+                    preempt_enable_no_resched();
+                    _stp_warn ("_stp_gettimofday_ns seqlock timeout; see STP_TIMELOCK*");
+                    return 0;
+            }
+        ndelay(STP_TIMELOCKDELAY);
         seq = read_seqbegin(&time->lock);
         base = time->base_ns;
         last = time->base_cycles;
diff --git a/translate.cxx b/translate.cxx
index b4d727c72..483d779a7 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -5459,11 +5459,11 @@ translate_pass (systemtap_session& s)
       s.op->newline() << "#ifndef MAXACTION_INTERRUPTIBLE";
       s.op->newline() << "#define MAXACTION_INTERRUPTIBLE (MAXACTION * 10)";
       s.op->newline() << "#endif";
-      s.op->newline() << "#ifndef MAXTRYLOCK";
-      s.op->newline() << "#define MAXTRYLOCK MAXACTION";
-      s.op->newline() << "#endif";
       s.op->newline() << "#ifndef TRYLOCKDELAY";
-      s.op->newline() << "#define TRYLOCKDELAY 100";
+      s.op->newline() << "#define TRYLOCKDELAY 10 /* microseconds */";
+      s.op->newline() << "#endif";
+      s.op->newline() << "#ifndef MAXTRYLOCK";
+      s.op->newline() << "#define MAXTRYLOCK 100 /* 1 millisecond total */";
       s.op->newline() << "#endif";
       s.op->newline() << "#ifndef MAXMAPENTRIES";
       s.op->newline() << "#define MAXMAPENTRIES 2048";