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Subject[PATCHv3] perf tools: Add struct ordered_events_buffer layer
On Mon, Aug 27, 2018 at 08:24:56AM -0700, Stephane Eranian wrote:

SNIP

> > - /* First entry is abused to maintain the to_free list. */
> > - oe->buffer_idx = 2;
> > - new = oe->buffer + 1;
> > + oe->buffer_idx = 1;
> > + new = &oe->buffer->event[0];
> > } else {
> > pr("allocation limit reached %" PRIu64 "B\n", oe->max_alloc_size);
>
>
> I am wondering about the usefulness of returning a new_event with
> new_event->event = NULL
> in this case. Don't you need new_event->event? If so, then you need return NULL.

yep, that's a bug.. with new being NULL in here,
we'd get a crash anyway.. so 'return NULL;' it is

SNIP

> > + * yet, we need to free only allocated ones ...
> > + */
> > + list_del(&oe->buffer->list);
> > + ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
> > +
> > + /* ... and continue with the rest */
> > + list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {
> > + list_del(&buffer->list);
> > + ordered_events_buffer__free(buffer, MAX_SAMPLE_BUFFER, oe);
>
>
> Here you are saying that if it is on the to_free list and not the
> current buffer, then necessarily
> all the entries have been used and it is safe to use
> MAX_SAMPLE_BUFFER. Is that right?

yes, at this point they either holds an event or NULL
so it's free to call __free_dup_event on it

thanks, v3 attached

added also Namhyung's ack, as the 'return NULL' change wasn't
related to the v2 changes

jirka


---
When ordering events, we use preallocated buffers to store separated
events. Those buffers currently don't have their own struct, but since
they are basically array of 'struct ordered_event' objects, we use the
first event to hold buffers data - list head, that holds all buffers
together:

struct ordered_events {
...
struct ordered_event *buffer;
...
};

struct ordered_event {
u64 timestamp;
u64 file_offset;
union perf_event *event;
struct list_head list;
};

This is quite convoluted and error prone as demonstrated by
free-ing issue discovered and fixed by Stephane in here [1].

This patch adds the 'struct ordered_events_buffer' object,
that holds the buffer data and frees it up properly.

[1] - https://marc.info/?l=linux-kernel&m=153376761329335&w=2

Reported-by: Stephane Eranian <eranian@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-qrkcqm5m1sugy4q83pfn5a1r@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/perf/util/ordered-events.c | 83 +++++++++++++++++++++++++++-----
tools/perf/util/ordered-events.h | 37 ++++++++------
2 files changed, 91 insertions(+), 29 deletions(-)

diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
index bad9e0296e9a..87171e8fd70d 100644
--- a/tools/perf/util/ordered-events.c
+++ b/tools/perf/util/ordered-events.c
@@ -80,14 +80,20 @@ static union perf_event *dup_event(struct ordered_events *oe,
return oe->copy_on_queue ? __dup_event(oe, event) : event;
}

-static void free_dup_event(struct ordered_events *oe, union perf_event *event)
+static void __free_dup_event(struct ordered_events *oe, union perf_event *event)
{
- if (event && oe->copy_on_queue) {
+ if (event) {
oe->cur_alloc_size -= event->header.size;
free(event);
}
}

+static void free_dup_event(struct ordered_events *oe, union perf_event *event)
+{
+ if (oe->copy_on_queue)
+ __free_dup_event(oe, event);
+}
+
#define MAX_SAMPLE_BUFFER (64 * 1024 / sizeof(struct ordered_event))
static struct ordered_event *alloc_event(struct ordered_events *oe,
union perf_event *event)
@@ -100,15 +106,43 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
if (!new_event)
return NULL;

+ /*
+ * We maintain following scheme of buffers for ordered
+ * event allocation:
+ *
+ * to_free list -> buffer1 (64K)
+ * buffer2 (64K)
+ * ...
+ *
+ * Each buffer keeps an array of ordered events objects:
+ * buffer -> event[0]
+ * event[1]
+ * ...
+ *
+ * Each allocated ordered event is linked to one of
+ * following lists:
+ * - time ordered list 'events'
+ * - list of currently removed events 'cache'
+ *
+ * Allocation of the ordered event uses following order
+ * to get the memory:
+ * - use recently removed object from 'cache' list
+ * - use available object in current allocation buffer
+ * - allocate new buffer if the current buffer is full
+ *
+ * Removal of ordered event object moves it from events to
+ * the cache list.
+ */
if (!list_empty(cache)) {
new = list_entry(cache->next, struct ordered_event, list);
list_del(&new->list);
} else if (oe->buffer) {
- new = oe->buffer + oe->buffer_idx;
+ new = &oe->buffer->event[oe->buffer_idx];
if (++oe->buffer_idx == MAX_SAMPLE_BUFFER)
oe->buffer = NULL;
} else if (oe->cur_alloc_size < oe->max_alloc_size) {
- size_t size = MAX_SAMPLE_BUFFER * sizeof(*new);
+ size_t size = sizeof(*oe->buffer) +
+ MAX_SAMPLE_BUFFER * sizeof(*new);

oe->buffer = malloc(size);
if (!oe->buffer) {
@@ -122,11 +156,11 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
oe->cur_alloc_size += size;
list_add(&oe->buffer->list, &oe->to_free);

- /* First entry is abused to maintain the to_free list. */
- oe->buffer_idx = 2;
- new = oe->buffer + 1;
+ oe->buffer_idx = 1;
+ new = &oe->buffer->event[0];
} else {
pr("allocation limit reached %" PRIu64 "B\n", oe->max_alloc_size);
+ return NULL;
}

new->event = new_event;
@@ -300,15 +334,38 @@ void ordered_events__init(struct ordered_events *oe, ordered_events__deliver_t d
oe->deliver = deliver;
}

+static void
+ordered_events_buffer__free(struct ordered_events_buffer *buffer,
+ unsigned int max, struct ordered_events *oe)
+{
+ if (oe->copy_on_queue) {
+ unsigned int i;
+
+ for (i = 0; i < max; i++)
+ __free_dup_event(oe, buffer->event[i].event);
+ }
+
+ free(buffer);
+}
+
void ordered_events__free(struct ordered_events *oe)
{
- while (!list_empty(&oe->to_free)) {
- struct ordered_event *event;
+ struct ordered_events_buffer *buffer, *tmp;

- event = list_entry(oe->to_free.next, struct ordered_event, list);
- list_del(&event->list);
- free_dup_event(oe, event->event);
- free(event);
+ if (list_empty(&oe->to_free))
+ return;
+
+ /*
+ * Current buffer might not have all the events allocated
+ * yet, we need to free only allocated ones ...
+ */
+ list_del(&oe->buffer->list);
+ ordered_events_buffer__free(oe->buffer, oe->buffer_idx, oe);
+
+ /* ... and continue with the rest */
+ list_for_each_entry_safe(buffer, tmp, &oe->to_free, list) {
+ list_del(&buffer->list);
+ ordered_events_buffer__free(buffer, MAX_SAMPLE_BUFFER, oe);
}
}

diff --git a/tools/perf/util/ordered-events.h b/tools/perf/util/ordered-events.h
index 8c7a2948593e..1338d5c345dc 100644
--- a/tools/perf/util/ordered-events.h
+++ b/tools/perf/util/ordered-events.h
@@ -25,23 +25,28 @@ struct ordered_events;
typedef int (*ordered_events__deliver_t)(struct ordered_events *oe,
struct ordered_event *event);

+struct ordered_events_buffer {
+ struct list_head list;
+ struct ordered_event event[0];
+};
+
struct ordered_events {
- u64 last_flush;
- u64 next_flush;
- u64 max_timestamp;
- u64 max_alloc_size;
- u64 cur_alloc_size;
- struct list_head events;
- struct list_head cache;
- struct list_head to_free;
- struct ordered_event *buffer;
- struct ordered_event *last;
- ordered_events__deliver_t deliver;
- int buffer_idx;
- unsigned int nr_events;
- enum oe_flush last_flush_type;
- u32 nr_unordered_events;
- bool copy_on_queue;
+ u64 last_flush;
+ u64 next_flush;
+ u64 max_timestamp;
+ u64 max_alloc_size;
+ u64 cur_alloc_size;
+ struct list_head events;
+ struct list_head cache;
+ struct list_head to_free;
+ struct ordered_events_buffer *buffer;
+ struct ordered_event *last;
+ ordered_events__deliver_t deliver;
+ int buffer_idx;
+ unsigned int nr_events;
+ enum oe_flush last_flush_type;
+ u32 nr_unordered_events;
+ bool copy_on_queue;
};

int ordered_events__queue(struct ordered_events *oe, union perf_event *event,
--
2.17.1
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