#include <linux/oom.h>
#include <asm/local.h>
-#include <asm/local64.h>
static void update_pages_handler(struct work_struct *work);
RB_CTX_MAX
};
+#if BITS_PER_LONG == 32
+#define RB_TIME_32
+#endif
+
+/* To test on 64 bit machines */
+//#define RB_TIME_32
+
+#ifdef RB_TIME_32
+
+struct rb_time_struct {
+ local_t cnt;
+ local_t top;
+ local_t bottom;
+};
+#else
+#include <asm/local64.h>
+struct rb_time_struct {
+ local64_t time;
+};
+#endif
+typedef struct rb_time_struct rb_time_t;
+
/*
* head_page == tail_page && head == tail then buffer is empty.
*/
size_t shortest_full;
unsigned long read;
unsigned long read_bytes;
- local64_t write_stamp;
- local64_t before_stamp;
+ rb_time_t write_stamp;
+ rb_time_t before_stamp;
u64 read_stamp;
/* ring buffer pages to update, > 0 to add, < 0 to remove */
long nr_pages_to_update;
int missed_events;
};
+#ifdef RB_TIME_32
+
+/*
+ * On 32 bit machines, local64_t is very expensive. As the ring
+ * buffer doesn't need all the features of a true 64 bit atomic,
+ * on 32 bit, it uses these functions (64 still uses local64_t).
+ *
+ * For the ring buffer, 64 bit required operations for the time is
+ * the following:
+ *
+ * - Only need 59 bits (uses 60 to make it even).
+ * - Reads may fail if it interrupted a modification of the time stamp.
+ * It will succeed if it did not interrupt another write even if
+ * the read itself is interrupted by a write.
+ * It returns whether it was successful or not.
+ *
+ * - Writes always succeed and will overwrite other writes and writes
+ * that were done by events interrupting the current write.
+ *
+ * - A write followed by a read of the same time stamp will always succeed,
+ * but may not contain the same value.
+ *
+ * - A cmpxchg will fail if it interrupted another write or cmpxchg.
+ * Other than that, it acts like a normal cmpxchg.
+ *
+ * The 60 bit time stamp is broken up by 30 bits in a top and bottom half
+ * (bottom being the least significant 30 bits of the 60 bit time stamp).
+ *
+ * The two most significant bits of each half holds a 2 bit counter (0-3).
+ * Each update will increment this counter by one.
+ * When reading the top and bottom, if the two counter bits match then the
+ * top and bottom together make a valid 60 bit number.
+ */
+#define RB_TIME_SHIFT 30
+#define RB_TIME_VAL_MASK ((1 << RB_TIME_SHIFT) - 1)
+
+static inline int rb_time_cnt(unsigned long val)
+{
+ return (val >> RB_TIME_SHIFT) & 3;
+}
+
+static inline u64 rb_time_val(unsigned long top, unsigned long bottom)
+{
+ u64 val;
+
+ val = top & RB_TIME_VAL_MASK;
+ val <<= RB_TIME_SHIFT;
+ val |= bottom & RB_TIME_VAL_MASK;
+
+ return val;
+}
+
+static inline bool __rb_time_read(rb_time_t *t, u64 *ret, unsigned long *cnt)
+{
+ unsigned long top, bottom;
+ unsigned long c;
+
+ /*
+ * If the read is interrupted by a write, then the cnt will
+ * be different. Loop until both top and bottom have been read
+ * without interruption.
+ */
+ do {
+ c = local_read(&t->cnt);
+ top = local_read(&t->top);
+ bottom = local_read(&t->bottom);
+ } while (c != local_read(&t->cnt));
+
+ *cnt = rb_time_cnt(top);
+
+ /* If top and bottom counts don't match, this interrupted a write */
+ if (*cnt != rb_time_cnt(bottom))
+ return false;
+
+ *ret = rb_time_val(top, bottom);
+ return true;
+}
+
+static bool rb_time_read(rb_time_t *t, u64 *ret)
+{
+ unsigned long cnt;
+
+ return __rb_time_read(t, ret, &cnt);
+}
+
+static inline unsigned long rb_time_val_cnt(unsigned long val, unsigned long cnt)
+{
+ return (val & RB_TIME_VAL_MASK) | ((cnt & 3) << RB_TIME_SHIFT);
+}
+
+static inline void rb_time_split(u64 val, unsigned long *top, unsigned long *bottom)
+{
+ *top = (unsigned long)((val >> RB_TIME_SHIFT) & RB_TIME_VAL_MASK);
+ *bottom = (unsigned long)(val & RB_TIME_VAL_MASK);
+}
+
+static inline void rb_time_val_set(local_t *t, unsigned long val, unsigned long cnt)
+{
+ val = rb_time_val_cnt(val, cnt);
+ local_set(t, val);
+}
+
+static void rb_time_set(rb_time_t *t, u64 val)
+{
+ unsigned long cnt, top, bottom;
+
+ rb_time_split(val, &top, &bottom);
+
+ /* Writes always succeed with a valid number even if it gets interrupted. */
+ do {
+ cnt = local_inc_return(&t->cnt);
+ rb_time_val_set(&t->top, top, cnt);
+ rb_time_val_set(&t->bottom, bottom, cnt);
+ } while (cnt != local_read(&t->cnt));
+}
+
+static inline bool
+rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set)
+{
+ unsigned long ret;
+
+ ret = local_cmpxchg(l, expect, set);
+ return ret == expect;
+}
+
+static int rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
+{
+ unsigned long cnt, top, bottom;
+ unsigned long cnt2, top2, bottom2;
+ u64 val;
+
+ /* The cmpxchg always fails if it interrupted an update */
+ if (!__rb_time_read(t, &val, &cnt2))
+ return false;
+
+ if (val != expect)
+ return false;
+
+ cnt = local_read(&t->cnt);
+ if ((cnt & 3) != cnt2)
+ return false;
+
+ cnt2 = cnt + 1;
+
+ rb_time_split(val, &top, &bottom);
+ top = rb_time_val_cnt(top, cnt);
+ bottom = rb_time_val_cnt(bottom, cnt);
+
+ rb_time_split(set, &top2, &bottom2);
+ top2 = rb_time_val_cnt(top2, cnt2);
+ bottom2 = rb_time_val_cnt(bottom2, cnt2);
+
+ if (!rb_time_read_cmpxchg(&t->cnt, cnt, cnt2))
+ return false;
+ if (!rb_time_read_cmpxchg(&t->top, top, top2))
+ return false;
+ if (!rb_time_read_cmpxchg(&t->bottom, bottom, bottom2))
+ return false;
+ return true;
+}
+
+#else /* 64 bits */
+
+/* local64_t always succeeds */
+
+static inline bool rb_time_read(rb_time_t *t, u64 *ret)
+{
+ *ret = local64_read(&t->time);
+ return true;
+}
+static void rb_time_set(rb_time_t *t, u64 val)
+{
+ local64_set(&t->time, val);
+}
+
+static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
+{
+ u64 val;
+ val = local64_cmpxchg(&t->time, expect, set);
+ return val == expect;
+}
+#endif
+
/**
* ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
* @buffer: The ring_buffer to get the number of pages from
delta = rb_time_delta(event);
- write_stamp = local64_read(&cpu_buffer->write_stamp);
+ if (!rb_time_read(&cpu_buffer->write_stamp, &write_stamp))
+ return 0;
/* Make sure the write stamp is read before testing the location */
barrier();
unsigned long write_mask =
local_read(&bpage->write) & ~RB_WRITE_MASK;
unsigned long event_length = rb_event_length(event);
- u64 ret;
- ret = local64_cmpxchg(&cpu_buffer->write_stamp, write_stamp, write_stamp - delta);
/* Something came in, can't discard */
- if (ret != write_stamp)
+ if (!rb_time_cmpxchg(&cpu_buffer->write_stamp,
+ write_stamp, write_stamp - delta))
return 0;
/*
rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
struct rb_event_info *info)
{
+ u64 write_stamp;
+
WARN_ONCE(info->delta > (1ULL << 59),
KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
(unsigned long long)info->delta,
(unsigned long long)info->ts,
- (unsigned long long)local64_read(&cpu_buffer->write_stamp),
+ (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
sched_clock_stable() ? "" :
"If you just came from a suspend/resume,\n"
"please switch to the trace global clock:\n"
struct buffer_page *tail_page;
unsigned long tail, write, w;
u64 before, after;
+ bool a_ok;
+ bool b_ok;
/* Don't let the compiler play games with cpu_buffer->tail_page */
tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
/*A*/ w = local_read(&tail_page->write) & RB_WRITE_MASK;
barrier();
- before = local64_read(&cpu_buffer->before_stamp);
- after = local64_read(&cpu_buffer->write_stamp);
+ b_ok = rb_time_read(&cpu_buffer->before_stamp, &before);
+ a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
barrier();
info->ts = rb_time_stamp(cpu_buffer->buffer);
info->delta = info->ts - after;
}
- if (unlikely(test_time_stamp(info->delta))) {
- rb_check_timestamp(cpu_buffer, info);
- info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+ if (likely(a_ok && b_ok)) {
+ if (unlikely(test_time_stamp(info->delta))) {
+ rb_check_timestamp(cpu_buffer, info);
+ info->add_timestamp |= RB_ADD_STAMP_EXTEND;
+ }
}
/*
* If interrupting an event time update, we may need an absolute timestamp.
* Don't bother if this is the start of a new page (w == 0).
*/
- if (unlikely(before != after && w))
+ if (unlikely(!a_ok || !b_ok || (before != after && w)))
info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
/*
if (unlikely(info->add_timestamp))
info->length += RB_LEN_TIME_EXTEND;
- /*B*/ local64_set(&cpu_buffer->before_stamp, info->ts);
+ /*B*/ rb_time_set(&cpu_buffer->before_stamp, info->ts);
/*C*/ write = local_add_return(info->length, &tail_page->write);
if (unlikely(write > BUF_PAGE_SIZE)) {
if (tail != w) {
/* before and after may now different, fix it up*/
- before = local64_read(&cpu_buffer->before_stamp);
- after = local64_read(&cpu_buffer->write_stamp);
- if (before != after)
- (void)local64_cmpxchg(&cpu_buffer->before_stamp, before, after);
+ b_ok = rb_time_read(&cpu_buffer->before_stamp, &before);
+ a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+ if (a_ok && b_ok && before != after)
+ (void)rb_time_cmpxchg(&cpu_buffer->before_stamp, before, after);
}
return rb_move_tail(cpu_buffer, tail, info);
}
if (likely(tail == w)) {
u64 save_before;
+ bool s_ok;
/* Nothing interrupted us between A and C */
- /*D*/ local64_set(&cpu_buffer->write_stamp, info->ts);
+ /*D*/ rb_time_set(&cpu_buffer->write_stamp, info->ts);
barrier();
- /*E*/ save_before = local64_read(&cpu_buffer->before_stamp);
+ /*E*/ s_ok = rb_time_read(&cpu_buffer->before_stamp, &save_before);
+ RB_WARN_ON(cpu_buffer, !s_ok);
if (likely(!(info->add_timestamp &
(RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
/* This did not interrupt any time update */
if (unlikely(info->ts != save_before)) {
/* SLOW PATH - Interrupted between C and E */
- after = local64_read(&cpu_buffer->write_stamp);
+ a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+ RB_WARN_ON(cpu_buffer, !a_ok);
+
/* Write stamp must only go forward */
if (save_before > after) {
/*
* We do not care about the result, only that
* it gets updated atomically.
*/
- (void)local64_cmpxchg(&cpu_buffer->write_stamp, after, save_before);
+ (void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, save_before);
}
}
} else {
u64 ts;
/* SLOW PATH - Interrupted between A and C */
- after = local64_read(&cpu_buffer->write_stamp);
+ a_ok = rb_time_read(&cpu_buffer->write_stamp, &after);
+ /* Was interrupted before here, write_stamp must be valid */
+ RB_WARN_ON(cpu_buffer, !a_ok);
ts = rb_time_stamp(cpu_buffer->buffer);
barrier();
/*E*/ if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
after < ts) {
/* Nothing came after this event between C and E */
info->delta = ts - after;
- (void)local64_cmpxchg(&cpu_buffer->write_stamp, after, info->ts);
+ (void)rb_time_cmpxchg(&cpu_buffer->write_stamp, after, info->ts);
info->ts = ts;
} else {
/*
cpu_buffer->read = 0;
cpu_buffer->read_bytes = 0;
- local64_set(&cpu_buffer->write_stamp, 0);
- local64_set(&cpu_buffer->before_stamp, 0);
+ rb_time_set(&cpu_buffer->write_stamp, 0);
+ rb_time_set(&cpu_buffer->before_stamp, 0);
cpu_buffer->lost_events = 0;
cpu_buffer->last_overrun = 0;
projects / users / jedix / linux-maple.git / commitdiff