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SubjectRe: [PATCH] perf session: Add option to copy events when queueing
On 9/14/13 10:16 AM, Frederic Weisbecker wrote:
>> @@ -676,7 +682,12 @@ int perf_session_queue_event(struct perf_session *s, union perf_event *event,
>>
>> new->timestamp = timestamp;
>> new->file_offset = file_offset;
>> - new->event = event;
>> +
>> + if (s->copy_on_queue) {
>> + new->event = malloc(event->header.size);
>> + memcpy(new->event, event, event->header.size);
>> + } else
>> + new->event = event;

---8<---

> So do you think it should stay optional? This looks like a global problem, I mean
> the event can be unmapped anytime for any builtin tool mapping it, right?

Yes. I could make it the default behavior; just overhead in doing that
(malloc/copy for each event).

>
> Also we already allocate the sample list node (struct sample_queue) from os->sample
> buffer. ie: we have our own allocator there.
>
> Probably we should reuse that and include the copied event space in "struct sample_queue"?


Right, that's where I put the malloc and copy - I kept the relevant
change above. I take it you are thinking of something different but I am
not following you. You definitely do NOT want to change struct
sample_queue to include an event - like this:

diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 51f5edf..866944a 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -491,7 +491,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
struct sample_queue {
u64 timestamp;
u64 file_offset;
- union perf_event *event;
+ union perf_event event;
struct list_head list;
};

size of event is determined by mmap_event (mmap2_event in latest code)
which is > 4096 because of the filename argument. Including the event
directly in sample_queue would balloon memory usage (learned this the
hard way!).
>
> Also looking at it now, it seems we have a bug on the existing code:
>
>
> if (!list_empty(sc)) {
> new = list_entry(sc->next, struct sample_queue, list);
> list_del(&new->list);
> } else if (os->sample_buffer) {
> new = os->sample_buffer + os->sample_buffer_idx;
> if (++os->sample_buffer_idx == MAX_SAMPLE_BUFFER)
> os->sample_buffer = NULL;
> } else {
> os->sample_buffer = malloc(MAX_SAMPLE_BUFFER * sizeof(*new));
> if (!os->sample_buffer)
> return -ENOMEM;
> list_add(&os->sample_buffer->list, &os->to_free);
> os->sample_buffer_idx = 2;
> new = os->sample_buffer + 1;
> }
>
> If we actually run out of buffer rooms, we should realloc right after and not
> wait for the next entry, otherwise we loose an event:
>
> if (!list_empty(sc)) {
> new = list_entry(sc->next, struct sample_queue, list);
> list_del(&new->list);
> } else {
> if (os->sample_buffer) {
> new = os->sample_buffer + os->sample_buffer_idx;
> if (++os->sample_buffer_idx == MAX_SAMPLE_BUFFER)
> os->sample_buffer = NULL;
> }
>
> if (!os->sample_buffer) {
> os->sample_buffer = malloc(MAX_SAMPLE_BUFFER * sizeof(*new));
> if (!os->sample_buffer)
> return -ENOMEM;
> list_add(&os->sample_buffer->list, &os->to_free);
> os->sample_buffer_idx = 2;
> new = os->sample_buffer + 1;
> }
>
>
> Although the mirrored os->sample_buffer condition check is a bit ugly and should move to
> a function. But the idea is there.

Ok. That should be a separate patch. Are you going to submit that one?

David



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