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

Waiman Long
2014-09-30T16:49:20Z

On 09/30/2014 11:21 AM, Arnaldo Carvalho de Melo wrote:
> 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.

If I don't add the kernel name check, I will get a warning every time I
run mem recording with the workloads that I am using. So it is happening
in the current code. I think the short name may be different. I will do
more test to find out. If that is the case, an alternative is to do a
short name comparison if the long name match.

>> + }
>> + 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

Yes, you are right. I should do the casting in dso__find_by_longname().
Please make the adjustment.

Thanks,
Longman