Em Wed, Sep 24, 2014 at 11:45:40AM -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 <[email protected]>
> ---
> tools/perf/util/dso.c | 73 ++++++++++++++++++++++++++++++++++++++++++--
> tools/perf/util/dso.h | 1 +
> tools/perf/util/machine.h | 4 ++-
> 3 files changed, 73 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index c2c6134..810a4b5 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -651,6 +651,67 @@ 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);
> + 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 */
> + /*
> + * The kernel DSOs may have duplicated long name,
> + * so don't print warning for them.
> + */
> + if (!warned && !strstr(name, "kernel.kallsyms")
> + && !strstr(name, "/vmlinux")) {
> + pr_warning("Duplicated dso long name: %s\n",
> + name);
Huh? Can you elaborate on this? Ho can we add multiple DSOs with the
exact same name into this tree? Have you actually seen this in practice?
I guess so, judging by the comment above ("may have").
I'll try the patch to see if I get these warnings...
But initial reaction to these long casts and fallbacking to pointer
arithmetic for tree searching/inserting looked ugly :-\
- Arnaldo
> + 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->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)
> @@ -754,6 +815,7 @@ struct dso *dso__new(const char *name)
> dso->kernel = DSO_TYPE_USER;
> dso->needs_swap = DSO_SWAP__UNSET;
> dso->dsos = NULL;
> + RB_CLEAR_NODE(&dso->rb_node);
> INIT_LIST_HEAD(&dso->node);
> INIT_LIST_HEAD(&dso->data.open_entry);
> }
> @@ -776,6 +838,11 @@ void dso__delete(struct dso *dso)
> zfree((char **)&dso->long_name);
> dso->long_name_allocated = false;
> }
> + if (dso->dsos) {
> + /* Remove entry from rbtree */
> + rb_erase(&dso->rb_node, &dso->dsos->root);
> + dso->dsos = NULL;
> + }
>
> dso__data_close(dso);
> dso_cache__free(&dso->data.cache);
> @@ -854,6 +921,7 @@ void dsos__add(struct dsos *dsos, struct dso *dso)
> {
> dso->dsos = dsos;
> 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 +935,7 @@ 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);
> }
>
> struct dso *__dsos__findnew(struct dsos *dsos, const char *name)
> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
> index cadfef7..bae7042 100644
> --- a/tools/perf/util/dso.h
> +++ b/tools/perf/util/dso.h
> @@ -94,6 +94,7 @@ struct dsos;
>
> struct dso {
> struct list_head node;
> + struct rb_node rb_node; /* rbtree node sorted by long name */
> struct dsos *dsos;
> struct rb_root symbols[MAP__NR_TYPES];
> struct rb_root symbol_names[MAP__NR_TYPES];
> diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
> index d8abb6c..f7546f3 100644
> --- a/tools/perf/util/machine.h
> +++ b/tools/perf/util/machine.h
> @@ -23,10 +23,12 @@ extern const char *ref_reloc_sym_names[];
> struct vdso_info;
>
> /*
> - * DSOs are put into a list for fast iteration.
> + * DSOs are put into both a list for fast iteration and rbtree for fast
> + * long name lookup.
> */
> struct dsos {
> struct list_head head;
> + struct rb_root root; /* rbtree root sorted by long name */
> };
>
> struct machine {
> --
> 1.7.1
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