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Subject[PATCH 33/37] perf tools: Add front cache for dso data access
Date
There's a high contention in dso_cache__find() due to the dso->lock
when dwarf unwinding is done with libunwind. Add last accessed
pointers of dso_cache to lockless lookup. It'll fallback to normal
tree search when it misses the last cache.

The size 16 is arbitrary and works best for my setting.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/dso.c | 28 ++++++++++++++++++++++++++--
tools/perf/util/dso.h | 2 ++
2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 6c1f5619f423..d8ee1fd826e7 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -466,12 +466,31 @@ dso_cache__free(struct dso *dso)
pthread_mutex_unlock(&dso->lock);
}

+static void update_last_cache(struct dso *dso, struct dso_cache *cache)
+{
+ int i;
+
+ for (i = DSO_LAST_CACHE_NR - 1; i > 0; i--)
+ dso->data.last[i] = dso->data.last[i-1];
+
+ dso->data.last[0] = cache;
+}
+
static struct dso_cache *dso_cache__find(struct dso *dso, u64 offset)
{
const struct rb_root *root = &dso->data.cache;
struct rb_node * const *p = &root->rb_node;
const struct rb_node *parent = NULL;
struct dso_cache *cache;
+ int i;
+
+ for (i = 0; i < DSO_LAST_CACHE_NR; i++) {
+ cache = dso->data.last[i];
+
+ if (cache && cache->offset <= offset &&
+ offset < cache->offset + DSO__DATA_CACHE_SIZE)
+ return cache;
+ }

pthread_mutex_lock(&dso->lock);
while (*p != NULL) {
@@ -485,8 +504,10 @@ static struct dso_cache *dso_cache__find(struct dso *dso, u64 offset)
p = &(*p)->rb_left;
else if (offset >= end)
p = &(*p)->rb_right;
- else
+ else {
+ update_last_cache(dso, cache);
goto out;
+ }
}
cache = NULL;
out:
@@ -515,13 +536,16 @@ dso_cache__insert(struct dso *dso, struct dso_cache *new)
p = &(*p)->rb_left;
else if (offset >= end)
p = &(*p)->rb_right;
- else
+ else {
+ update_last_cache(dso, cache);
goto out;
+ }
}

rb_link_node(&new->rb_node, parent, p);
rb_insert_color(&new->rb_node, root);

+ update_last_cache(dso, new);
cache = NULL;
out:
pthread_mutex_unlock(&dso->lock);
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index c18fcc0e8081..28e8bb320495 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -136,6 +136,8 @@ struct dso {
/* dso data file */
struct {
struct rb_root cache;
+#define DSO_LAST_CACHE_NR 16
+ struct dso_cache *last[DSO_LAST_CACHE_NR];
int fd;
int status;
u32 status_seen;
--
2.1.3


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