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[Qemu-devel] [PULL 12/13] qht-bench: add -p flag to precompute hash valu
From: |
Richard Henderson |
Subject: |
[Qemu-devel] [PULL 12/13] qht-bench: add -p flag to precompute hash values |
Date: |
Wed, 26 Sep 2018 11:37:08 -0700 |
From: "Emilio G. Cota" <address@hidden>
Precomputing the hash values allows us to perform more frequent
accesses to the hash table, thereby reaching higher throughputs.
We keep the old behaviour by default, since (1) we might confuse
users if they measured a speedup without changing anything in
the QHT implementation, and (2) benchmarking the hash function
"on line" is also valuable.
Before:
$ taskset -c 0 tests/qht-bench -n 1
Throughput: 38.18 MT/s
After:
$ taskset -c 0 tests/qht-bench -n 1
Throughput: 38.16 MT/s
After (with precomputing):
$ taskset -c 0 tests/qht-bench -n 1 -p
Throughput: 50.87 MT/s
Signed-off-by: Emilio G. Cota <address@hidden>
Signed-off-by: Richard Henderson <address@hidden>
---
tests/qht-bench.c | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
diff --git a/tests/qht-bench.c b/tests/qht-bench.c
index f492b3a20a..2089e2bed1 100644
--- a/tests/qht-bench.c
+++ b/tests/qht-bench.c
@@ -53,6 +53,7 @@ static unsigned long resize_delay = 1000;
static double resize_rate; /* 0.0 to 1.0 */
static unsigned int n_rz_threads = 1;
static QemuThread *rz_threads;
+static bool precompute_hash;
static double update_rate; /* 0.0 to 1.0 */
static uint64_t update_threshold;
@@ -101,11 +102,18 @@ static bool is_equal(const void *ap, const void *bp)
return *a == *b;
}
-static inline uint32_t h(unsigned long v)
+static uint32_t h(unsigned long v)
{
return tb_hash_func7(v, 0, 0, 0, 0);
}
+static uint32_t hval(unsigned long v)
+{
+ return v;
+}
+
+static uint32_t (*hfunc)(unsigned long v) = h;
+
/*
* From: https://en.wikipedia.org/wiki/Xorshift
* This is faster than rand_r(), and gives us a wider range (RAND_MAX is only
@@ -149,7 +157,7 @@ static void do_rw(struct thread_info *info)
bool read;
p = &keys[info->r & (lookup_range - 1)];
- hash = h(*p);
+ hash = hfunc(*p);
read = qht_lookup(&ht, p, hash);
if (read) {
stats->rd++;
@@ -158,7 +166,7 @@ static void do_rw(struct thread_info *info)
}
} else {
p = &keys[info->r & (update_range - 1)];
- hash = h(*p);
+ hash = hfunc(*p);
if (info->write_op) {
bool written = false;
@@ -289,7 +297,9 @@ static void htable_init(void)
/* avoid allocating memory later by allocating all the keys now */
keys = g_malloc(sizeof(*keys) * n);
for (i = 0; i < n; i++) {
- keys[i] = populate_offset + i;
+ long val = populate_offset + i;
+
+ keys[i] = precompute_hash ? h(val) : hval(val);
}
/* some sanity checks */
@@ -321,7 +331,7 @@ static void htable_init(void)
r = xorshift64star(r);
p = &keys[r & (init_range - 1)];
- hash = h(*p);
+ hash = hfunc(*p);
if (qht_insert(&ht, p, hash, NULL)) {
break;
}
@@ -412,7 +422,7 @@ static void parse_args(int argc, char *argv[])
int c;
for (;;) {
- c = getopt(argc, argv, "d:D:g:k:K:l:hn:N:o:r:Rs:S:u:");
+ c = getopt(argc, argv, "d:D:g:k:K:l:hn:N:o:pr:Rs:S:u:");
if (c < 0) {
break;
}
@@ -451,6 +461,10 @@ static void parse_args(int argc, char *argv[])
case 'o':
populate_offset = atol(optarg);
break;
+ case 'p':
+ precompute_hash = true;
+ hfunc = hval;
+ break;
case 'r':
update_range = pow2ceil(atol(optarg));
break;
--
2.17.1
- [Qemu-devel] [PULL 00/13] tcg-next patch queue, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 01/13] qht: remove unused map param from qht_remove__locked, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 02/13] qht: add qht_iter_remove, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 03/13] test-qht: test qht_iter_remove, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 04/13] test-qht: test removal of non-existent entries, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 12/13] qht-bench: add -p flag to precompute hash values,
Richard Henderson <=
- [Qemu-devel] [PULL 07/13] qht: drop ht argument from qht iterators, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 13/13] tcg/i386: fix vector operations on 32-bit hosts, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 09/13] qht: constify qht_lookup, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 06/13] test-qht: speed up + test qht_resize, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 08/13] qht: fix comment in qht_bucket_remove_entry, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 11/13] qht: constify arguments to some internal functions, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 10/13] qht: constify qht_statistics_init, Richard Henderson, 2018/09/26
- [Qemu-devel] [PULL 05/13] test-qht: test deletion of the last entry in a bucket, Richard Henderson, 2018/09/26