[Xen-devel] [PATCH] add printf_ratelimit to tame the wild prints

[Steven Rostedt <srostedt@xxxxxxxxxx>]

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@xxxxxxxxxx>

Index: xen/arch/x86/mm.c
===================================================================
--- xen.orig/arch/x86/mm.c
+++ xen/arch/x86/mm.c
@@ -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
Index: xen/drivers/char/console.c
===================================================================
--- xen.orig/drivers/char/console.c
+++ xen/drivers/char/console.c
@@ -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: Andy Kleen (net_ratelimit)
+ *     Ported to Xen - Steven Rostedt - Red Hat
  */
 
 #include <stdarg.h>
@@ -420,6 +424,52 @@ 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);
+}
 
 /*
  * **************************************************************
Index: xen/include/xen/lib.h
===================================================================
--- xen.orig/include/xen/lib.h
+++ xen/include/xen/lib.h
@@ -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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