Re: [PATCH v5 2/2] perf tool: improves DSO long names lookup speed with rbtree

Arnaldo Carvalho de Melo
2014-09-30T15:22:04Z

Em Mon, Sep 29, 2014 at 04:07:29PM -0400, Waiman Long escreveu:
> With workload that spawns and destroys many threads and processes,
> it was found that perf-mem could took a long time to post-process
> the perf data after the target workload had completed its operation.
> The performance bottleneck was found to be the lookup and insertion
> of the new DSO structures (thousands of them in this case).
>
> In a dual-socket Ivy-Bridge E7-4890 v2 machine (30-core, 60-thread),
> the perf profile below shows what perf was doing after the profiled
> AIM7 shared workload completed:
>
> - 83.94% perf libc-2.11.3.so [.] __strcmp_sse42
> - __strcmp_sse42
> - 99.82% map__new
> machine__process_mmap_event
> perf_session_deliver_event
> perf_session__process_event
> __perf_session__process_events
> cmd_record
> cmd_mem
> run_builtin
> main
> __libc_start_main
> - 13.17% perf perf [.] __dsos__findnew
> __dsos__findnew
> map__new
> machine__process_mmap_event
> perf_session_deliver_event
> perf_session__process_event
> __perf_session__process_events
> cmd_record
> cmd_mem
> run_builtin
> main
> __libc_start_main
>
> So about 97% of CPU times were spent in the map__new() function
> trying to insert new DSO entry into the DSO linked list. The whole
> post-processing step took about 9 minutes.
>
> The DSO structures are currently searched linearly. So the total
> processing time will be proportional to n^2.
>
> To overcome this performance problem, the DSO code is modified to
> also put the DSO structures in a RB tree sorted by its long name
> in additional to being in a simple linked list. With this change,
> the processing time will become proportional to n*log(n) which will
> be much quicker for large n. However, the short name will still be
> searched using the old linear searching method. With that patch
> in place, the same perf-mem post-processing step took less than 30
> seconds to complete.
>
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
> ---
> tools/perf/util/dso.c | 72 ++++++++++++++++++++++++++++++++++++++++++--
> tools/perf/util/dso.h | 1 +
> tools/perf/util/machine.c | 1 +
> tools/perf/util/machine.h | 4 ++-
> 4 files changed, 73 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 901a58f..9a81c03 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -653,6 +653,67 @@ struct dso *dso__kernel_findnew(struct machine *machine, const char *name,
> return dso;
> }
>
> +/*
> + * Find a matching entry and/or link current entry to RB tree.
> + * Either one of the dso or name parameter must be non-NULL or the
> + * function will not work.
> + */
> +static struct dso *dso__findlink_by_longname(struct rb_root *root,
> + struct dso *dso, const char *name)
> +{
> + struct rb_node **p = &root->rb_node;
> + struct rb_node *parent = NULL;
> + int warned = false;
> +
> + if (!name)
> + name = dso->long_name;
> + /*
> + * Find node with the matching name
> + */
> + while (*p) {
> + struct dso *this = rb_entry(*p, struct dso, rb_node);
> + int rc = strcmp(name, this->long_name);
> +
> + parent = *p;
> + if (rc == 0) {
> + /*
> + * In case the new DSO is a duplicate of an existing
> + * one, print an one-time warning & put the new entry
> + * at the end of the list of duplicates.
> + */
> + if (!dso || (dso == this))
> + return this; /* Find matching dso */
> + /*
> + * The core kernel DSOs may have duplicated long name.
> + * (See dso__load_sym()). Don't print warning for them.
> + */
> + if (!warned && !strstr(name, "kernel.kallsyms")
> + && !strstr(name, "/vmlinux")) {
> + pr_warning("Duplicated dso long name: %s\n",
> + name);
> + warned = true;

I still wonder if in this case we should just return, i.e. why would we
want to have multiple entries with the same name here? Anyway, I guess
it doesn't hurt, right?

Something to be further investigated to find a better solution, but I
guess that the patch as-is now should provide that speedup without
introducing any new oddities. Will apply.

> + }
> + rc = 1;
> + }
> + if (rc < 0)
> + p = &parent->rb_left;
> + else
> + p = &parent->rb_right;
> + }
> + if (dso) {
> + /* Add new node and rebalance tree */
> + rb_link_node(&dso->rb_node, parent, p);
> + rb_insert_color(&dso->rb_node, root);
> + }
> + return NULL;
> +}
> +
> +static inline struct dso *
> +dso__find_by_longname(struct rb_root *root, const char *name)
> +{
> + return dso__findlink_by_longname(root, NULL, name);
> +}
> +
> void dso__set_long_name(struct dso *dso, const char *name, bool name_allocated)
> {
> if (name == NULL)
> @@ -755,6 +816,7 @@ struct dso *dso__new(const char *name)
> dso->a2l_fails = 1;
> dso->kernel = DSO_TYPE_USER;
> dso->needs_swap = DSO_SWAP__UNSET;
> + RB_CLEAR_NODE(&dso->rb_node);
> INIT_LIST_HEAD(&dso->node);
> INIT_LIST_HEAD(&dso->data.open_entry);
> }
> @@ -765,6 +827,10 @@ struct dso *dso__new(const char *name)
> void dso__delete(struct dso *dso)
> {
> int i;
> +
> + if (!RB_EMPTY_NODE(&dso->rb_node))
> + pr_err("DSO %s is still in rbtree when being deleted!\n",
> + dso->long_name);
> for (i = 0; i < MAP__NR_TYPES; ++i)
> symbols__delete(&dso->symbols[i]);
>
> @@ -854,6 +920,7 @@ bool __dsos__read_build_ids(struct list_head *head, bool with_hits)
> void dsos__add(struct dsos *dsos, struct dso *dso)
> {
> list_add_tail(&dso->node, &dsos->head);
> + dso__findlink_by_longname(&dsos->root, dso, NULL);
> }
>
> struct dso *dsos__find(const struct dsos *dsos, const char *name,
> @@ -867,10 +934,7 @@ struct dso *dsos__find(const struct dsos *dsos, const char *name,
> return pos;
> return NULL;
> }
> - list_for_each_entry(pos, &dsos->head, node)
> - if (strcmp(pos->long_name, name) == 0)
> - return pos;
> - return NULL;
> + return dso__find_by_longname((struct rb_root *)&dsos->root, name);

Why do you need this cast? Humm, because in the end it will get to a
function that either does insertion or does a simple search. Ok, I think
that dso__find_by_longname is the closest to that thing where the cast
should be applied, after making dso__find_by_longname receive a const
rb_root pointer.

I.e. the dso__find_by_longname name implies it will not change any of
its parameters, its supposed to be a simple search. I will do this
change while applying it.

- Arnaldo