* [PATCH 1/2] trace-cmd: Make a global tracecmd_quick_hash() instead of a local knuth_hash()
2019-09-20 15:15 [PATCH 0/2] trace-cmd/kernel-shark: Use one quick hash algorithm Steven Rostedt
@ 2019-09-20 15:15 ` Steven Rostedt
2019-09-20 15:15 ` [PATCH 2/2] kernel-shark: Increase the size of the task hash Steven Rostedt
1 sibling, 0 replies; 4+ messages in thread
From: Steven Rostedt @ 2019-09-20 15:15 UTC (permalink / raw)
To: linux-trace-devel; +Cc: Yordan Karadzhov
From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
As the 32 bit Knuth algorith produces the same results as the small
sizes[1], create a single algorithm that takes in a @bits parameter that
will return a masked result. And replace the local version of knuth_hash()
used by the trace-cmd filter code. This will also be used to remove other
copies of knuth_hash().
[1] https://lore.kernel.org/r/20190829114913.5df4ced9@gandalf.local.home
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
include/trace-cmd/trace-filter-hash.h | 24 ++++++++++++++++++++++++
lib/trace-cmd/trace-filter-hash.c | 20 +++++---------------
2 files changed, 29 insertions(+), 15 deletions(-)
diff --git a/include/trace-cmd/trace-filter-hash.h b/include/trace-cmd/trace-filter-hash.h
index e94bc87d1e1d..4111c41eeb2d 100644
--- a/include/trace-cmd/trace-filter-hash.h
+++ b/include/trace-cmd/trace-filter-hash.h
@@ -19,6 +19,30 @@ struct tracecmd_filter_id {
int count;
};
+/**
+ * tracecmd_quick_hash - A quick (non secured) hash alogirthm
+ * @val: The value to perform the hash on
+ * @bits: The size in bits you need to return
+ *
+ * This is a quick 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
+ * 2^32.
+ *
+ * @bits is used to max the result for use cases that require
+ * a power of 2 return value that is less than 32 bits. Any value
+ * of @bits greater than 31 (or zero), will simply return the full hash on @val.
+ */
+static inline uint32_t tracecmd_quick_hash(uint32_t val, unsigned int bits)
+{
+ val *= UINT32_C(2654435761);
+
+ if (!bits || bits > 31)
+ return val;
+
+ return val & ((1 << bits) - 1);
+}
+
struct tracecmd_filter_id_item *
tracecmd_filter_id_find(struct tracecmd_filter_id *hash, int id);
void tracecmd_filter_id_add(struct tracecmd_filter_id *hash, int id);
diff --git a/lib/trace-cmd/trace-filter-hash.c b/lib/trace-cmd/trace-filter-hash.c
index 45ca68c2959e..f5f0fb09403b 100644
--- a/lib/trace-cmd/trace-filter-hash.c
+++ b/lib/trace-cmd/trace-filter-hash.c
@@ -12,23 +12,13 @@
#include "trace-filter-hash.h"
-#define FILTER_HASH_SIZE 256
-
-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);
-}
+#define FILTER_HASH_BITS 8
+#define FILTER_HASH_SIZE (1 << FILTER_HASH_BITS)
struct tracecmd_filter_id_item *
tracecmd_filter_id_find(struct tracecmd_filter_id *hash, int id)
{
- int key = knuth_hash(id);
+ int key = tracecmd_quick_hash(id, FILTER_HASH_BITS);
struct tracecmd_filter_id_item *item = hash->hash[key];
while (item) {
@@ -42,7 +32,7 @@ tracecmd_filter_id_find(struct tracecmd_filter_id *hash, int id)
void tracecmd_filter_id_add(struct tracecmd_filter_id *hash, int id)
{
- int key = knuth_hash(id);
+ int key = tracecmd_quick_hash(id, FILTER_HASH_BITS);
struct tracecmd_filter_id_item *item;
item = calloc(1, sizeof(*item));
@@ -57,7 +47,7 @@ void tracecmd_filter_id_add(struct tracecmd_filter_id *hash, int id)
void tracecmd_filter_id_remove(struct tracecmd_filter_id *hash, int id)
{
- int key = knuth_hash(id);
+ int key = tracecmd_quick_hash(id, FILTER_HASH_BITS);
struct tracecmd_filter_id_item **next = &hash->hash[key];
struct tracecmd_filter_id_item *item;
--
2.20.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH 2/2] kernel-shark: Increase the size of the task hash
2019-09-20 15:15 [PATCH 0/2] trace-cmd/kernel-shark: Use one quick hash algorithm Steven Rostedt
2019-09-20 15:15 ` [PATCH 1/2] trace-cmd: Make a global tracecmd_quick_hash() instead of a local knuth_hash() Steven Rostedt
@ 2019-09-20 15:15 ` Steven Rostedt
2019-09-20 15:47 ` Yordan Karadzhov (VMware)
1 sibling, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2019-09-20 15:15 UTC (permalink / raw)
To: linux-trace-devel; +Cc: Yordan Karadzhov
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
^ permalink raw reply related [flat|nested] 4+ messages in thread