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Merge remote-tracking branch 'stefanha/tracing' into staging

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# By Markus Armbruster
# Via Stefan Hajnoczi
* stefanha/tracing:
  trace: Fix location of simpletrace.py in docs
  trace: Clean up the "try to update atomic until it worked" loops
  trace: Direct access of atomics is verboten, use the API
  trace: Fix simple trace dropped event record for big endian
This commit is contained in:
Anthony Liguori 2013-02-06 16:36:16 -06:00
commit 5b2cd9857d
2 changed files with 18 additions and 25 deletions
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4
docs/tracing.txt
View File

@ -23,7 +23,7 @@ for debugging, profiling, and observing execution.
4. Pretty-print the binary trace file:
./simpletrace.py trace-events trace-*
./scripts/simpletrace.py trace-events trace-*
== Trace events ==
@ -198,7 +198,7 @@ The "simple" backend produces binary trace files that can be formatted with the
simpletrace.py script. The script takes the "trace-events" file and the binary
trace:
./simpletrace.py trace-events trace-12345
./scripts/simpletrace.py trace-events trace-12345
You must ensure that the same "trace-events" file was used to build QEMU,
otherwise trace event declarations may have changed and output will not be

39
trace/simple.c
View File

@ -53,7 +53,7 @@ enum {
uint8_t trace_buf[TRACE_BUF_LEN];
static unsigned int trace_idx;
static unsigned int writeout_idx;
static uint64_t dropped_events;
static int dropped_events;
static FILE *trace_fp;
static char *trace_file_name;
@ -63,7 +63,7 @@ typedef struct {
uint64_t timestamp_ns;
uint32_t length; /* in bytes */
uint32_t reserved; /* unused */
uint8_t arguments[];
uint64_t arguments[];
} TraceRecord;
typedef struct {
@ -160,25 +160,22 @@ static gpointer writeout_thread(gpointer opaque)
uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
} dropped;
unsigned int idx = 0;
uint64_t dropped_count;
int dropped_count;
size_t unused __attribute__ ((unused));
for (;;) {
wait_for_trace_records_available();
if (dropped_events) {
if (g_atomic_int_get(&dropped_events)) {
dropped.rec.event = DROPPED_EVENT_ID,
dropped.rec.timestamp_ns = get_clock();
dropped.rec.length = sizeof(TraceRecord) + sizeof(dropped_events),
dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
dropped.rec.reserved = 0;
while (1) {
dropped_count = dropped_events;
if (g_atomic_int_compare_and_exchange((gint *)&dropped_events,
dropped_count, 0)) {
break;
}
}
memcpy(dropped.rec.arguments, &dropped_count, sizeof(uint64_t));
do {
dropped_count = g_atomic_int_get(&dropped_events);
} while (!g_atomic_int_compare_and_exchange(&dropped_events,
dropped_count, 0));
dropped.rec.arguments[0] = dropped_count;
unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
}
@ -213,22 +210,17 @@ int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasi
uint32_t rec_len = sizeof(TraceRecord) + datasize;
uint64_t timestamp_ns = get_clock();
while (1) {
old_idx = trace_idx;
do {
old_idx = g_atomic_int_get(&trace_idx);
smp_rmb();
new_idx = old_idx + rec_len;
if (new_idx - writeout_idx > TRACE_BUF_LEN) {
/* Trace Buffer Full, Event dropped ! */
g_atomic_int_inc((gint *)&dropped_events);
g_atomic_int_inc(&dropped_events);
return -ENOSPC;
}
if (g_atomic_int_compare_and_exchange((gint *)&trace_idx,
old_idx, new_idx)) {
break;
}
}
} while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
idx = old_idx % TRACE_BUF_LEN;
@ -275,7 +267,8 @@ void trace_record_finish(TraceBufferRecord *rec)
record.event |= TRACE_RECORD_VALID;
write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
if ((trace_idx - writeout_idx) > TRACE_BUF_FLUSH_THRESHOLD) {
if ((g_atomic_int_get(&trace_idx) - writeout_idx)
> TRACE_BUF_FLUSH_THRESHOLD) {
flush_trace_file(false);
}
}