debugtrace: add per-cpu buffer option

debugtrace is normally writing trace entries into a single trace
buffer. There are cases where this is not optimal, e.g. when hunting
a bug which requires writing lots of trace entries and one cpu is
stuck. This will result in other cpus filling the trace buffer and
finally overwriting the interesting trace entries of the hanging cpu.

In order to be able to debug such situations add the capability to use
per-cpu trace buffers. This can be selected by specifying the
debugtrace boot parameter with the modifier "cpu:", like:

  debugtrace=cpu:16

At the same time switch the parsing function to accept size modifiers
(e.g. 4M or 1G).

Printing out the trace entries is done for each buffer in order to
minimize the effort needed during printing. As each entry is prefixed
with its sequence number sorting the entries can easily be done when
analyzing them.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 7c72e31032bd7130d640d32afd8224ec061d3a24..832797e2e2b82d331e3193b2c0781608edc6d038 100644 (file)
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -644,12 +644,13 @@ over the PCI busses sequentially) or by PCI device (must be on segment 0).
 Limits the number lines printed in Xen stack traces.
 
 ### debugtrace
-> `= <integer>`
+> `= [cpu:]<size>`
 
 > Default: `128`
 
-Specify the size of the console debug trace buffer in KiB. The debug
-trace feature is only enabled in debugging builds of Xen.
+Specify the size of the console debug trace buffer. By specifying `cpu:`
+additionally a trace buffer of the specified size is allocated per cpu.
+The debug trace feature is only enabled in debugging builds of Xen.
 
 ### dma_bits
 > `= <integer>`

diff --git a/xen/common/debugtrace.c b/xen/common/debugtrace.c
index a66aa39103e5d9125c7a9596c64007b50e12bf46..9b60c9595923adf1fd8f4e6d3306a651f6145392 100644 (file)
--- a/xen/common/debugtrace.c
+++ b/xen/common/debugtrace.c
@@ -6,6 +6,7 @@
 
 
 #include <xen/console.h>
+#include <xen/cpu.h>
 #include <xen/init.h>
 #include <xen/keyhandler.h>
 #include <xen/lib.h>
@@ -23,35 +24,79 @@ struct debugtrace_data {
 };
 
 static struct debugtrace_data *dt_data;
+static DEFINE_PER_CPU(struct debugtrace_data *, dt_cpu_data);
 
-static unsigned int debugtrace_kilobytes = 128;
-static unsigned long debugtrace_bytes;
+static unsigned long __read_mostly debugtrace_bytes = 128 << 10;
+static bool __read_mostly debugtrace_per_cpu;
 static bool debugtrace_buf_empty = true;
 static bool debugtrace_used;
 static DEFINE_SPINLOCK(debugtrace_lock);
-integer_param("debugtrace", debugtrace_kilobytes);
 
-static void debugtrace_dump_worker(void)
+static int __init debugtrace_parse_param(const char *s)
 {
-    if ( !debugtrace_used )
+    unsigned long bytes;
+
+    if ( !strncmp(s, "cpu:", 4) )
+    {
+        debugtrace_per_cpu = true;
+        s += 4;
+    }
+    bytes = parse_size_and_unit(s, &s);
+
+    if ( *s )
+        return -EINVAL;
+
+    debugtrace_bytes = MAX(bytes, PAGE_SIZE);
+
+    /* Round size down to next power of two. */
+    while ( (bytes = (debugtrace_bytes & (debugtrace_bytes - 1))) != 0 )
+        debugtrace_bytes = bytes;
+
+    return 0;
+}
+custom_param("debugtrace", debugtrace_parse_param);
+
+static void debugtrace_dump_buffer(struct debugtrace_data *data,
+                                   const char *which)
+{
+    if ( !data )
         return;
 
-    printk("debugtrace_dump() starting\n");
+    printk("debugtrace_dump() %s buffer starting\n", which);
 
     /* Print oldest portion of the ring. */
-    if ( dt_data->buf[dt_data->prd] != '\0' )
-        console_serial_puts(&dt_data->buf[dt_data->prd],
-                            debugtrace_bytes - dt_data->prd);
+    if ( data->buf[data->prd] != '\0' )
+        console_serial_puts(&data->buf[data->prd],
+                            debugtrace_bytes - data->prd);
 
     /* Print youngest portion of the ring. */
-    dt_data->buf[dt_data->prd] = '\0';
-    console_serial_puts(&dt_data->buf[0], dt_data->prd);
+    data->buf[data->prd] = '\0';
+    console_serial_puts(&data->buf[0], data->prd);
 
-    memset(dt_data->buf, '\0', debugtrace_bytes);
-    dt_data->prd = 0;
-    debugtrace_buf_empty = true;
+    memset(data->buf, '\0', debugtrace_bytes);
+    data->prd = 0;
 
-    printk("debugtrace_dump() finished\n");
+    printk("debugtrace_dump() %s buffer finished\n", which);
+}
+
+static void debugtrace_dump_worker(void)
+{
+    unsigned int cpu;
+
+    if ( !debugtrace_used )
+        return;
+
+    debugtrace_dump_buffer(dt_data, "global");
+
+    for ( cpu = 0; cpu < nr_cpu_ids; cpu++ )
+    {
+        char buf[16];
+
+        snprintf(buf, sizeof(buf), "cpu %u", cpu);
+        debugtrace_dump_buffer(per_cpu(dt_cpu_data, cpu), buf);
+    }
+
+    debugtrace_buf_empty = true;
 }
 
 static void debugtrace_toggle(void)
@@ -91,28 +136,33 @@ void debugtrace_dump(void)
 
 static void debugtrace_add_to_buf(char *buf)
 {
+    struct debugtrace_data *data;
     char *p;
 
+    data = debugtrace_per_cpu ? this_cpu(dt_cpu_data) : dt_data;
+
     for ( p = buf; *p != '\0'; p++ )
     {
-        dt_data->buf[dt_data->prd++] = *p;
-        if ( dt_data->prd == debugtrace_bytes )
-            dt_data->prd = 0;
+        data->buf[data->prd++] = *p;
+        if ( data->prd == debugtrace_bytes )
+            data->prd = 0;
     }
 }
 
 void debugtrace_printk(const char *fmt, ...)
 {
     static char buf[1024], last_buf[1024];
-    static unsigned int count, last_count;
+    static unsigned int count, last_count, last_cpu;
     static unsigned long last_prd;
 
     char          cntbuf[24];
     va_list       args;
     unsigned long flags;
     unsigned int nr;
+    struct debugtrace_data *data;
 
-    if ( !dt_data )
+    data = debugtrace_per_cpu ? this_cpu(dt_cpu_data) : dt_data;
+    if ( !data )
         return;
 
     debugtrace_used = true;
@@ -132,17 +182,20 @@ void debugtrace_printk(const char *fmt, ...)
     }
     else
     {
-        if ( debugtrace_buf_empty || strcmp(buf, last_buf) )
+        unsigned int cpu = debugtrace_per_cpu ? smp_processor_id() : 0;
+
+        if ( debugtrace_buf_empty || cpu != last_cpu || strcmp(buf, last_buf) )
         {
             debugtrace_buf_empty = false;
-            last_prd = dt_data->prd;
+            last_prd = data->prd;
             last_count = ++count;
+            last_cpu = cpu;
             safe_strcpy(last_buf, buf);
             snprintf(cntbuf, sizeof(cntbuf), "%u ", count);
         }
         else
         {
-            dt_data->prd = last_prd;
+            data->prd = last_prd;
             snprintf(cntbuf, sizeof(cntbuf), "%u-%u ", last_count, ++count);
         }
         debugtrace_add_to_buf(cntbuf);
@@ -157,34 +210,69 @@ static void debugtrace_key(unsigned char key)
     debugtrace_toggle();
 }
 
-static int __init debugtrace_init(void)
+static void debugtrace_alloc_buffer(struct debugtrace_data **ptr,
+                                    unsigned int cpu)
 {
     int order;
-    unsigned long kbytes;
     struct debugtrace_data *data;
 
-    /* Round size down to next power of two. */
-    while ( (kbytes = (debugtrace_kilobytes & (debugtrace_kilobytes-1))) != 0 )
-        debugtrace_kilobytes = kbytes;
-
-    debugtrace_bytes = debugtrace_kilobytes << 10;
-    if ( debugtrace_bytes == 0 )
-        return 0;
+    if ( *ptr )
+        return;
 
     order = get_order_from_bytes(debugtrace_bytes);
     data = alloc_xenheap_pages(order, 0);
     if ( !data )
-        return -ENOMEM;
+    {
+        if ( debugtrace_per_cpu )
+            printk("CPU%u: failed to allocate debugtrace buffer\n", cpu);
+        else
+            printk("failed to allocate debugtrace buffer\n");
+        return;
+    }
 
-    debugtrace_bytes = PAGE_SIZE << order;
-    memset(data, '\0', debugtrace_bytes);
-    debugtrace_bytes -= sizeof(*data);
+    memset(data, '\0', debugtrace_bytes + sizeof(*data));
 
     dt_data = data;
+    *ptr = data;
+}
+
+static int debugtrace_cpu_callback(struct notifier_block *nfb,
+                                   unsigned long action, void *hcpu)
+{
+    unsigned int cpu = (unsigned long)hcpu;
+
+    /* Buffers are only ever allocated, never freed. */
+    if ( action == CPU_UP_PREPARE )
+        debugtrace_alloc_buffer(&per_cpu(dt_cpu_data, cpu), cpu);
+
+    return 0;
+}
+
+static struct notifier_block debugtrace_nfb = {
+    .notifier_call = debugtrace_cpu_callback
+};
+
+static int __init debugtrace_init(void)
+{
+    unsigned int cpu;
+
+    if ( !debugtrace_bytes )
+        return 0;
 
     register_keyhandler('T', debugtrace_key,
                         "toggle debugtrace to console/buffer", 0);
 
+    debugtrace_bytes -= sizeof(struct debugtrace_data);
+
+    if ( debugtrace_per_cpu )
+    {
+        for_each_online_cpu ( cpu )
+            debugtrace_alloc_buffer(&per_cpu(dt_cpu_data, cpu), cpu);
+        register_cpu_notifier(&debugtrace_nfb);
+    }
+    else
+        debugtrace_alloc_buffer(&dt_data, 0);
+
     return 0;
 }
 __initcall(debugtrace_init);