[PATCH] add printf_ratelimit

[PATCH] add printf_ratelimit

[Steven Rostedt]

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I sent this patch back on 9/19 and it never went anywhere.  I'm sending 
it again, against the lastest unstable.

-- Steve

==== Originally sent 9/19/2006 ====

If someone turns on verbose and/or debug the hypervisor slams the serial 
pretty badly when starting a FV domain.  So I pulled the 
printk_ratelimit from Linux and put it into the hypervisor.  Right now 
the only user of it is the MEM_LOG in arch/x86/mm.c which can really 
spit out a lot.

Since printk_ratelimit is very helpful in the Linux kernel, I can see it 
being also used in HV.  I changed it slightly from Linux to match the 
naming convention in Xen.  Since printk is defined to printf, I declared 
the function printf_ratelimit and made a define of printk_ratelimit to 
just be a clone of printf_ratelimit.

-- Steve

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

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diff -r f0302ed1ac62 xen/arch/x86/mm.c
--- a/xen/arch/x86/mm.c	Mon Oct 02 11:47:55 2006 -0400
+++ b/xen/arch/x86/mm.c	Mon Oct 02 11:48:22 2006 -0400
@@ -109,9 +109,13 @@
 #include <public/memory.h>
 
 #ifdef VERBOSE
-#define MEM_LOG(_f, _a...)                                  \
-  printk("DOM%u: (file=mm.c, line=%d) " _f "\n",            \
-         current->domain->domain_id , __LINE__ , ## _a )
+#define MEM_LOG(_f, _a...)                                          \
+    do {                                                            \
+        if (printk_ratelimit()) {                                   \
+            printk("DOM%u: (file=mm.c, line=%d) " _f "\n",          \
+                   current->domain->domain_id , __LINE__ , ## _a ); \
+                }                                                   \
+    } while (0)
 #else
 #define MEM_LOG(_f, _a...) ((void)0)
 #endif
diff -r f0302ed1ac62 xen/drivers/char/console.c
--- a/xen/drivers/char/console.c	Mon Oct 02 11:47:55 2006 -0400
+++ b/xen/drivers/char/console.c	Mon Oct 02 11:48:22 2006 -0400
@@ -4,6 +4,10 @@
  * Emergency console I/O for Xen and the domain-0 guest OS.
  * 
  * Copyright (c) 2002-2004, K A Fraser.
+ *
+ * Added printf_ratelimit
+ *     Taken from Linux - Author: Andi Kleen (net_ratelimit)
+ *     Ported to Xen - Steven Rostedt - Red Hat
  */
 
 #include <stdarg.h>
@@ -465,6 +469,52 @@ int console_getc(void)
     return serial_getc(sercon_handle);
 }
 
+/*
+ * printk rate limiting, lifted from Linux.
+ *
+ * This enforces a rate limit: not more than one kernel message
+ * every printf_ratelimit_jiffies.
+ */
+int __printf_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
+{
+	static DEFINE_SPINLOCK(ratelimit_lock);
+	static unsigned long toks = 10 * 5 * HZ;
+	static unsigned long last_msg;
+	static int missed;
+	unsigned long flags;
+	unsigned long now = jiffies;
+
+	spin_lock_irqsave(&ratelimit_lock, flags);
+	toks += now - last_msg;
+	last_msg = now;
+	if (toks > (ratelimit_burst * ratelimit_jiffies))
+		toks = ratelimit_burst * ratelimit_jiffies;
+	if (toks >= ratelimit_jiffies) {
+		int lost = missed;
+
+		missed = 0;
+		toks -= ratelimit_jiffies;
+		spin_unlock_irqrestore(&ratelimit_lock, flags);
+		if (lost)
+			printk("printk: %d messages suppressed.\n", lost);
+		return 1;
+	}
+	missed++;
+	spin_unlock_irqrestore(&ratelimit_lock, flags);
+	return 0;
+}
+
+/* minimum time in jiffies between messages */
+int printf_ratelimit_jiffies = 5 * HZ;
+
+/* number of messages we send before ratelimiting */
+int printf_ratelimit_burst = 10;
+
+int printf_ratelimit(void)
+{
+	return __printf_ratelimit(printf_ratelimit_jiffies,
+				printf_ratelimit_burst);
+}
 
 /*
  * **************************************************************
diff -r f0302ed1ac62 xen/include/xen/lib.h
--- a/xen/include/xen/lib.h	Mon Oct 02 11:47:55 2006 -0400
+++ b/xen/include/xen/lib.h	Mon Oct 02 11:48:22 2006 -0400
@@ -52,8 +52,11 @@ extern void debugtrace_printk(const char
 /* Allows us to use '%p' as general-purpose machine-word format char. */
 #define _p(_x) ((void *)(unsigned long)(_x))
 #define printk(_f , _a...) printf( _f , ## _a )
+#define printk_ratelimit() printf_ratelimit()
 extern void printf(const char *format, ...)
     __attribute__ ((format (printf, 1, 2)));
+extern int __printf_ratelimit(int ratelimit_jiffies, int ratelimit_burst);
+extern int printf_ratelimit(void);
 extern void panic(const char *format, ...)
     __attribute__ ((format (printf, 1, 2)));
 extern long vm_assist(struct domain *, unsigned int, unsigned int);

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Re: [PATCH] add printf_ratelimit

[Stephen C. Tweedie]

Hi,

On Mon, 2006-10-02 at 12:39 -0400, Steven Rostedt wrote:
> I sent this patch back on 9/19 and it never went anywhere.  I'm sending 
> it again, against the lastest unstable.

> If someone turns on verbose and/or debug the hypervisor slams the serial 
> pretty badly when starting a FV domain.  So I pulled the 
> printk_ratelimit from Linux and put it into the hypervisor.  Right now 
> the only user of it is the MEM_LOG in arch/x86/mm.c which can really 
> spit out a lot.

A *lot*.  With serial console, starting an HVM domain can take 30
seconds for me just because of these log messages.  Rate-limiting is
necessary for such cases.

--Stephen