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Date: Mon, 15 Sep 2014 17:15:44 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Waiman Long <Waiman.Long@...com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Paul Mackerras <paulus@...ba.org>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
Scott J Norton <scott.norton@...com>,
Don Zickus <dzickus@...hat.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH] perf mem: improves DSO long names search speed with RB
tree
Em Mon, Sep 15, 2014 at 12:43:21PM -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 searching 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
> put the DSO structures in a RB tree sorted by its long name. 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 which is slow.
> 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@...com>
> ---
> tools/perf/util/dso.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++--
> tools/perf/util/dso.h | 1 +
> 2 files changed, 74 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 819f104..bd92564 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -611,17 +611,83 @@ struct dso *dso__kernel_findnew(struct machine *machine, const char *name,
> return dso;
> }
>
> +/*
> + * RB root of DSOs sorted by the long name
> + */
> +static struct rb_root dso__long_name_root = { NULL };
> +
> +/*
> + * Either one of the dso or name parameter must be non-NULL or the
> + * function will not work.
> + */
> +static struct dso *
> +dso__long_name_findadd_node(struct dso *dso, const char *name)
> +{
> + struct rb_node **p = &dso__long_name_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, long_name_rb_node);
> + long rc = (long)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 & sort the entry
> + * by its DSO address.
> + */
> + if (!dso || (dso == this))
> + return this; /* Find matching dso */
> + if (!warned) {
> + pr_warning("Duplicated dso long name: %s\n",
> + name);
> + warned = true;
> + }
> + rc = (long)dso - (long)this;
> + }
> + if (rc < 0)
> + p = &parent->rb_left;
> + else
> + p = &parent->rb_right;
> + }
> + if (dso) {
> + /* Add new node and rebalance tree */
> + rb_link_node(&dso->long_name_rb_node, parent, p);
> + rb_insert_color(&dso->long_name_rb_node, &dso__long_name_root);
> + }
> + return NULL;
> +}
> +
> +static inline void dso__long_name_remove_node(struct dso *dso)
> +{
> + rb_erase(&dso->long_name_rb_node, &dso__long_name_root);
> +}
> +
> void dso__set_long_name(struct dso *dso, const char *name, bool name_allocated)
> {
> if (name == NULL)
> return;
>
> + if (dso->long_name) {
> + if (!strcmp(dso->long_name, name))
> + return;
> + dso__long_name_remove_node(dso);
> + }
> +
> if (dso->long_name_allocated)
> free((char *)dso->long_name);
>
> dso->long_name = name;
> dso->long_name_len = strlen(name);
> dso->long_name_allocated = name_allocated;
> + (void)dso__long_name_findadd_node(dso, name);
> }
>
> void dso__set_short_name(struct dso *dso, const char *name, bool name_allocated)
> @@ -695,6 +761,8 @@ struct dso *dso__new(const char *name)
> if (dso != NULL) {
> int i;
> strcpy(dso->name, name);
> + RB_CLEAR_NODE(&dso->long_name_rb_node);
> + dso->long_name = NULL;
> dso__set_long_name(dso, dso->name, false);
> dso__set_short_name(dso, dso->name, false);
> for (i = 0; i < MAP__NR_TYPES; ++i)
> @@ -733,6 +801,10 @@ void dso__delete(struct dso *dso)
> zfree((char **)&dso->long_name);
> dso->long_name_allocated = false;
> }
> + if (dso->long_name) {
> + dso__long_name_remove_node(dso);
> + dso->long_name = NULL;
> + }
>
> dso__data_close(dso);
> dso_cache__free(&dso->data.cache);
> @@ -822,10 +894,7 @@ struct dso *dsos__find(const struct list_head *head, const char *name, bool cmp_
> return pos;
> return NULL;
> }
> - list_for_each_entry(pos, head, node)
> - if (strcmp(pos->long_name, name) == 0)
> - return pos;
> - return NULL;
> + return dso__long_name_findadd_node(NULL, name);
By its name, dsos__find() should not add anything to any data structure,
it is about just finding something, or it would be named
dsos__findnew().
Also would we want to add something if we don't even have a DSO here?
I think the right thing is to call it dsos__find_by_longname() and have
a dsos__findnew_by_longname().
If you want to share code behind that api, probably there are
opportunities for that, but doing it at this level makes the code
unecessarily hard to follow :-\
- Arnaldo
> struct dso *__dsos__findnew(struct list_head *head, const char *name)
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index ad553ba..ed949e4 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -76,6 +76,7 @@ struct dso {
> struct list_head node;
> struct rb_root symbols[MAP__NR_TYPES];
> struct rb_root symbol_names[MAP__NR_TYPES];
> + struct rb_node long_name_rb_node;
> void *a2l;
> char *symsrc_filename;
> unsigned int a2l_fails;
> --
> 1.7.1
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