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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v2 4/4] xen: add per-cpu buffer option to debugtrace
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@xxxxxxxx>
---
V2: only allocate buffer if not already done so
---
docs/misc/xen-command-line.pandoc | 7 +-
xen/common/debugtrace.c | 145 +++++++++++++++++++++++++++++---------
2 files changed, 115 insertions(+), 37 deletions(-)
diff --git a/docs/misc/xen-command-line.pandoc
b/docs/misc/xen-command-line.pandoc
index 7c72e31032..832797e2e2 100644
--- 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 c0189267dd..94c95316c3 100644
--- 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>
@@ -24,30 +25,61 @@ struct debugtrace_data_s {
};
static struct debugtrace_data_s *debtr_data;
+static DEFINE_PER_CPU(struct debugtrace_data_s *, debtr_cpu_data);
-static unsigned int debugtrace_kilobytes = 128;
+static unsigned int debugtrace_bytes = 128 << 10;
+static bool debugtrace_per_cpu;
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 ( !strncmp(s, "cpu:", 4) )
+ {
+ debugtrace_per_cpu = true;
+ s += 4;
+ }
+ debugtrace_bytes = parse_size_and_unit(s, NULL);
+ return 0;
+}
+custom_param("debugtrace", debugtrace_parse_param);
+
+static void debugtrace_dump_buffer(struct debugtrace_data_s *data,
+ const char *which)
{
- if ( !debtr_data || !debugtrace_used )
+ if ( !data )
return;
- printk("debugtrace_dump() starting\n");
+ printk("debugtrace_dump() %s buffer starting\n", which);
/* Print oldest portion of the ring. */
- ASSERT(debtr_data->buf[debtr_data->bytes - 1] == 0);
- console_serial_puts(&debtr_data->buf[debtr_data->prd]);
+ ASSERT(data->buf[data->bytes - 1] == 0);
+ console_serial_puts(&data->buf[data->prd]);
/* Print youngest portion of the ring. */
- debtr_data->buf[debtr_data->prd] = '\0';
- console_serial_puts(&debtr_data->buf[0]);
+ data->buf[data->prd] = '\0';
+ console_serial_puts(&data->buf[0]);
+
+ memset(data->buf, '\0', data->bytes);
+
+ printk("debugtrace_dump() %s buffer finished\n", which);
+}
+
+static void debugtrace_dump_worker(void)
+{
+ unsigned int cpu;
+ char buf[16];
+
+ if ( !debugtrace_used )
+ return;
- memset(debtr_data->buf, '\0', debtr_data->bytes);
+ debugtrace_dump_buffer(debtr_data, "global");
- printk("debugtrace_dump() finished\n");
+ for ( cpu = 0; cpu < nr_cpu_ids; cpu++ )
+ {
+ snprintf(buf, sizeof(buf), "cpu %u", cpu);
+ debugtrace_dump_buffer(per_cpu(debtr_cpu_data, cpu), buf);
+ }
}
static void debugtrace_toggle(void)
@@ -87,34 +119,41 @@ void debugtrace_dump(void)
static void debugtrace_add_to_buf(char *buf)
{
+ struct debugtrace_data_s *data;
char *p;
+ data = debugtrace_per_cpu ? this_cpu(debtr_cpu_data) : debtr_data;
+
for ( p = buf; *p != '\0'; p++ )
{
- debtr_data->buf[debtr_data->prd++] = *p;
+ data->buf[data->prd++] = *p;
/* Always leave a nul byte at the end of the buffer. */
- if ( debtr_data->prd == (debtr_data->bytes - 1) )
- debtr_data->prd = 0;
+ if ( data->prd == (data->bytes - 1) )
+ data->prd = 0;
}
}
void debugtrace_printk(const char *fmt, ...)
{
static char buf[1024], last_buf[1024];
- static unsigned int count, last_count, last_prd;
+ static unsigned int count, last_count, last_prd, last_cpu;
char cntbuf[24];
va_list args;
unsigned long flags;
+ struct debugtrace_data_s *data;
+ unsigned int cpu;
- if ( !debtr_data )
+ data = debugtrace_per_cpu ? this_cpu(debtr_cpu_data) : debtr_data;
+ cpu = debugtrace_per_cpu ? smp_processor_id() : 0;
+ if ( !data )
return;
debugtrace_used = true;
spin_lock_irqsave(&debugtrace_lock, flags);
- ASSERT(debtr_data->buf[debtr_data->bytes - 1] == 0);
+ ASSERT(data->buf[data->bytes - 1] == 0);
va_start(args, fmt);
vsnprintf(buf, sizeof(buf), fmt, args);
@@ -128,16 +167,17 @@ void debugtrace_printk(const char *fmt, ...)
}
else
{
- if ( strcmp(buf, last_buf) )
+ if ( strcmp(buf, last_buf) || cpu != last_cpu )
{
- last_prd = debtr_data->prd;
+ last_prd = data->prd;
last_count = ++count;
+ last_cpu = cpu;
safe_strcpy(last_buf, buf);
snprintf(cntbuf, sizeof(cntbuf), "%u ", count);
}
else
{
- debtr_data->prd = last_prd;
+ data->prd = last_prd;
snprintf(cntbuf, sizeof(cntbuf), "%u-%u ", last_count, ++count);
}
debugtrace_add_to_buf(cntbuf);
@@ -152,33 +192,70 @@ static void debugtrace_key(unsigned char key)
debugtrace_toggle();
}
-static int __init debugtrace_init(void)
+static void debugtrace_alloc_buffer(struct debugtrace_data_s **ptr)
{
int order;
- unsigned long kbytes, bytes;
struct debugtrace_data_s *data;
- /* Round size down to next power of two. */
- while ( (kbytes = (debugtrace_kilobytes & (debugtrace_kilobytes-1))) != 0 )
- debugtrace_kilobytes = kbytes;
-
- bytes = debugtrace_kilobytes << 10;
- if ( bytes == 0 )
- return 0;
+ if ( debugtrace_bytes < PAGE_SIZE || *ptr )
+ return;
- order = get_order_from_bytes(bytes);
+ order = get_order_from_bytes(debugtrace_bytes);
data = alloc_xenheap_pages(order, 0);
if ( !data )
- return -ENOMEM;
+ {
+ printk("failed to allocate debugtrace buffer\n");
+ return;
+ }
+
+ memset(data, '\0', debugtrace_bytes);
+ data->bytes = debugtrace_bytes - sizeof(*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. */
+ switch ( action )
+ {
+ case CPU_UP_PREPARE:
+ debugtrace_alloc_buffer(&per_cpu(debtr_cpu_data, cpu));
+ break;
+ default:
+ break;
+ }
+ return 0;
+}
- memset(data, '\0', bytes);
+static struct notifier_block debugtrace_nfb = {
+ .notifier_call = debugtrace_cpu_callback
+};
+
+static int __init debugtrace_init(void)
+{
+ unsigned long bytes;
+ unsigned int cpu;
- data->bytes = bytes - sizeof(*data);
- debtr_data = data;
+ /* Round size down to next power of two. */
+ while ( (bytes = (debugtrace_bytes & (debugtrace_bytes - 1))) != 0 )
+ debugtrace_bytes = bytes;
register_keyhandler('T', debugtrace_key,
"toggle debugtrace to console/buffer", 0);
+ if ( debugtrace_per_cpu )
+ {
+ for_each_online_cpu ( cpu )
+ debugtrace_alloc_buffer(&per_cpu(debtr_cpu_data, cpu));
+ register_cpu_notifier(&debugtrace_nfb);
+ }
+ else
+ debugtrace_alloc_buffer(&debtr_data);
+
return 0;
}
__initcall(debugtrace_init);
--
2.16.4
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