A hack to speedup lockstat_read

79cbd037 · Silas Boyd-Wickizer · c8f0c10b · 79cbd037 · 79cbd037
--- a/lockstat.h
+++ b/lockstat.h
@@ -29,7 +29,7 @@ struct klockstat {
 #define LOCKSTAT_CLEAR     3

 // Debug knobs
-#define LOCKSTAT_BIO       0
+#define LOCKSTAT_BIO       1
 #define LOCKSTAT_CONDVAR   0
 #define LOCKSTAT_CONSOLE   1
 #define LOCKSTAT_CRANGE    1

--- a/spinlock.c
+++ b/spinlock.c
@@ -155,15 +155,26 @@ static int
 lockstat_read(struct inode *ip, char *dst, u32 off, u32 n)
 {
  static const u64 sz = sizeof(struct lockstat);
+  static struct {
+    struct klockstat *stat;
+    u32 off;
+  } cache;
+
  struct klockstat *stat;
  u32 cur;

  if (off % sz || n < sz)
    return -1;

-  cur = 0;
  acquire(&lockstat_lock);
-  LIST_FOREACH(stat, &lockstat_list, link) {
+  if (cache.off == off && cache.stat != NULL) {
+    cur = cache.off;
+    stat = cache.stat;
+  } else {
+    cur = 0;
+    stat = LIST_FIRST(&lockstat_list);
+  }
+  for (; stat != NULL; stat = LIST_NEXT(stat, link)) {
    struct lockstat *ls = &stat->s;
    if (n < sizeof(*ls))
      break;
@@ -176,7 +187,15 @@ lockstat_read(struct inode *ip, char *dst, u32 off, u32 n)
  }
  release(&lockstat_lock);

-  return cur >= off ? cur - off : 0;
+  if (cur < off) {
+    cache.off = 0;
+    cache.stat = NULL;
+    return 0;
+  }
+
+  cache.off = cur;
+  cache.stat = stat;
+  return cur - off;
 }

 static int