Re: [PATCHv2] perf tools: Add struct ordered_events_buffer layer
From: Stephane Eranian
Date: Mon Aug 27 2018 - 11:25:14 EST
Jiri,
On Mon, Aug 27, 2018 at 2:28 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> On Wed, Aug 15, 2018 at 10:48:25AM +0200, Jiri Olsa wrote:
> > On Tue, Aug 14, 2018 at 12:14:19AM -0700, Stephane Eranian wrote:
> >
> > SNIP
> >
> > > > @@ -104,11 +110,12 @@ static struct ordered_event *alloc_event(struct ordered_events *oe,
> > > > 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) {
> > > > @@ -122,9 +129,8 @@ 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];
> > >
> > > Ok, but I think this section between the malloc() and the line above
> > > needs some comments to clarify what is going on.
> > > It is still hard to read.
> >
> > ok, I put some bigger comment at the top, but I'm not too happy
> > feel free to suggest different one ;-)
> >
> > >
> > > > } else {
> > > > pr("allocation limit reached %" PRIu64 "B\n", oe->max_alloc_size);
> > > > }
> > > > @@ -300,15 +306,27 @@ 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,
> > > > + struct ordered_events *oe)
> > > > +{
> > > > + if (oe->copy_on_queue) {
> > > > + unsigned int i;
> > > > +
> > > > + for (i = 0; i < MAX_SAMPLE_BUFFER; i++)
> > > > + __free_dup_event(oe, buffer->event[i].event);
> > > > + }
> > > > +
> > > I have a problem with this one, given that the buffer->event[] is
> > > never actually zeroed.
> > > So what happens if you do not use all the entries by the time you have to free?
> > > I think one way to avoid this is by iterating only all the way to
> > > oe->buffer_idx.
> >
> > right, please check attached patch
>
> any comments? attaching v2
>
> thanks,
> 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@xxxxxxxxxx>
> Link: http://lkml.kernel.org/n/tip-qrkcqm5m1sugy4q83pfn5a1r@xxxxxxxxxxxxxx
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> tools/perf/util/ordered-events.c | 82 +++++++++++++++++++++++++++-----
> tools/perf/util/ordered-events.h | 37 +++++++-------
> 2 files changed, 90 insertions(+), 29 deletions(-)
>
> diff --git a/tools/perf/util/ordered-events.c b/tools/perf/util/ordered-events.c
> index bad9e0296e9a..3672060508a7 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) {
> @@ -122,9 +156,8 @@ 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);
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.
> }
> @@ -300,15 +333,38 @@ 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);
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?
> }
> }
>
> 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
>