vppinfra: optimize elog_string

Add a string hash to make sure that strings in the string table are
unique. This optimization has been coded piecemeal in multiple places,
we should have made the underlying function do the work years ago.

Ticket: VPP-1707
Type: fix

Change-Id: I5010fd4926b9b80ce3a168748f6de64e333ef498
Signed-off-by: Dave Barach <dave@barachs.net>

2 files changed, 33 insertions, 5 deletions

diff --git a/src/vppinfra/elog.c b/src/vppinfra/elog.c
index 6daed96719c..19d86bb70c0 100644
--- a/src/vppinfra/elog.c
+++ b/src/vppinfra/elog.c
@@ -508,6 +508,7 @@ elog_init (elog_main_t * em, u32 n_events)
   elog_track_register (em, &em->default_track);
 
   elog_time_now (&em->init_time);
+  em->string_table_hash = hash_create_string (0, sizeof (uword));
 }
 
 /* Returns number of events in ring and start index. */
@@ -561,16 +562,40 @@ u32
 elog_string (elog_main_t * em, char *fmt, ...)
 {
   u32 offset;
+  uword *p;
+  uword len;
   va_list va;
 
+  elog_lock (em);
+  vec_reset_length (em->string_table_tmp);
   va_start (va, fmt);
-  offset = vec_len (em->string_table);
-  em->string_table = (char *) va_format ((u8 *) em->string_table, fmt, &va);
+  em->string_table_tmp = va_format (em->string_table_tmp, fmt, &va);
   va_end (va);
 
-  /* Null terminate string if it is not already. */
-  if (vec_end (em->string_table)[-1] != 0)
-    vec_add1 (em->string_table, 0);
+  /* See if we already have this string in the string table */
+  p = hash_get_mem (em->string_table_hash, em->string_table_tmp);
+
+  /* We already have the string, so give the caller its offset */
+  if (p)
+    {
+      elog_unlock (em);
+      return (p[0]);
+    }
+
+  /* We don't, so add it. String table entries MUST be NULL terminated */
+  len = vec_len (em->string_table_tmp);
+  ASSERT (len > 0);
+  if (em->string_table_tmp[len - 1] != 0)
+    vec_add1 (em->string_table_tmp, 0);
+
+  offset = vec_len (em->string_table);
+  vec_append (em->string_table, em->string_table_tmp);
+
+  hash_set_mem (em->string_table_hash, em->string_table_tmp, offset);
+
+  /* We gave the key to the string table hash, so we can't reuse it! */
+  em->string_table_tmp = 0;
+  elog_unlock (em);
 
   return offset;
 }
diff --git a/src/vppinfra/elog.h b/src/vppinfra/elog.h
index 26352f7d608..3cd067ce707 100644
--- a/src/vppinfra/elog.h
+++ b/src/vppinfra/elog.h
@@ -53,6 +53,7 @@
 #include <vppinfra/error.h>	/* for ASSERT */
 #include <vppinfra/serialize.h>
 #include <vppinfra/time.h>	/* for clib_cpu_time_now */
+#include <vppinfra/hash.h>
 #include <vppinfra/mhash.h>
 
 typedef struct
@@ -155,6 +156,8 @@ typedef struct
 
   /** Events may refer to strings in string table. */
   char *string_table;
+  uword *string_table_hash;
+  u8 *string_table_tmp;
 
   /** Vector of tracks. */
   elog_track_t *tracks;