[PATCH 2/2] kernel-shark: Increase the size of the task hash

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

When loading a data file that contained 100,000s of tasks, using a 256
bucket size hash crippled it. By increasing the hash to 2^16 (65536) it
solves the issue (still small enough not to waste too much memory).

Also switched to the tracecmd_quick_hash() which is basically the same
as the local knuth_hash() function in libkshark.c.

Link: http://lore.kernel.org/linux-trace-devel/20190828140016.3ce1be4f@gandalf.local.home

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 kernel-shark/src/libkshark.c | 18 ++++--------------
 kernel-shark/src/libkshark.h |  3 ++-
 2 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/kernel-shark/src/libkshark.c b/kernel-shark/src/libkshark.c
index 4207ae6ffdb2..a36157835ce0 100644
--- a/kernel-shark/src/libkshark.c
+++ b/kernel-shark/src/libkshark.c
@@ -252,19 +252,8 @@ void kshark_free(struct kshark_context *kshark_ctx)
 	free(kshark_ctx);
 }
 
-static inline uint8_t knuth_hash(uint32_t val)
-{
-	/*
-	 * Small table hashing function adapted from Donald E. Knuth's 32 bit
-	 * multiplicative hash.  See The Art of Computer Programming (TAOCP).
-	 * Multiplication by the Prime number, closest to the golden ratio of
-	 * 2^8.
-	 */
-	return UINT8_C(val) * UINT8_C(157);
-}
-
 static struct kshark_task_list *
-kshark_find_task(struct kshark_context *kshark_ctx, uint8_t key, int pid)
+kshark_find_task(struct kshark_context *kshark_ctx, uint32_t key, int pid)
 {
 	struct kshark_task_list *list;
 
@@ -280,9 +269,10 @@ static struct kshark_task_list *
 kshark_add_task(struct kshark_context *kshark_ctx, int pid)
 {
 	struct kshark_task_list *list;
-	uint8_t key;
+	uint32_t key;
+
+	key = tracecmd_quick_hash(pid, KS_TASK_HASH_SHIFT);
 
-	key = knuth_hash(pid);
 	list = kshark_find_task(kshark_ctx, key, pid);
 	if (list)
 		return list;
diff --git a/kernel-shark/src/libkshark.h b/kernel-shark/src/libkshark.h
index 04e9cbfc71df..3407db197320 100644
--- a/kernel-shark/src/libkshark.h
+++ b/kernel-shark/src/libkshark.h
@@ -72,7 +72,8 @@ struct kshark_entry {
 };
 
 /** Size of the task's hash table. */
-#define KS_TASK_HASH_SIZE 256
+#define KS_TASK_HASH_SHIFT 16
+#define KS_TASK_HASH_SIZE (1 << KS_TASK_HASH_SHIFT)
 
 /** Linked list of tasks. */
 struct kshark_task_list {
-- 
2.20.1