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concurrent hopscotch hashtable only needs a load-load barrier in lookup

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and that is implied by the x86/x64's memory model ... avoiding the mfence instruction is a significant win

Signed-off-by: Erik Boasson <eb@ilities.com>
This commit is contained in:
Erik Boasson 2019-01-03 17:39:13 +01:00
parent 95f070d097
commit 771eed118b
4 changed files with 15 additions and 9 deletions
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11
src/util/src/ut_hopscotch.c
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@ -34,11 +34,7 @@ struct ut_chhBucket {
struct _Struct_size_bytes_(size) ut_chhBucketArray {
uint32_t size; /* power of 2 */
#if __STDC_VERSION__ >= 199901L
struct ut_chhBucket bs[];
#else
struct ut_chhBucket bs[1];
#endif
};
struct ut_chhBackingLock {
@ -91,9 +87,6 @@ static int ut_chhInit (struct ut_chh *rt, uint32_t init_size, ut_hhHash_fn hash,
for (i = 0; i < N_BACKING_LOCKS; i++) {
struct ut_chhBackingLock *s = &rt->backingLocks[i];
os_mutexInit (&s->lock);
}
for (i = 0; i < N_BACKING_LOCKS; i++) {
struct ut_chhBackingLock *s = &rt->backingLocks[i];
os_condInit (&s->cv, &s->lock);
}
for (i = 0; i < N_RESIZE_LOCKS; i++) {
@ -205,7 +198,7 @@ static void *ut_chhLookupInternal (struct ut_chhBucketArray const * const bsary,
do {
uint32_t hopinfo;
timestamp = os_atomic_ld32 (&bs[bucket].timestamp);
os_atomic_fence ();
os_atomic_fence_ldld ();
hopinfo = os_atomic_ld32 (&bs[bucket].hopinfo);
for (idx = 0; hopinfo != 0; hopinfo >>= 1, idx++) {
const uint32_t bidx = (bucket + idx) & idxmask;
@ -214,7 +207,7 @@ static void *ut_chhLookupInternal (struct ut_chhBucketArray const * const bsary,
return data;
}
}
os_atomic_fence ();
os_atomic_fence_ldld ();
} while (timestamp != os_atomic_ld32 (&bs[bucket].timestamp) && ++try_counter < CHH_MAX_TRIES);
if (try_counter == CHH_MAX_TRIES) {
/* Note: try_counter would not have been incremented to