weaselab/conflict-set
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Experiment with causing cache misses

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This commit is contained in:
Andrew Noyes
2024-09-10 22:06:00 -07:00
parent 0550fa0016
commit 814aac4ea7
1 changed files with 85 additions and 29 deletions
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114
ConflictSet.cpp
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@@ -48,6 +48,17 @@ limitations under the License.
#endif
#endif
#define SIM_CACHE_MISSES 0
#if SIM_CACHE_MISSES
constexpr void simCacheMiss(void *x) {
if (x) {
_mm_clflush(x);
}
}
#else
constexpr void simCacheMiss(void *) {}
#endif
#include <memcheck.h>
using namespace weaselab;
@@ -836,21 +847,29 @@ int getNodeIndex(Node16 *self, uint8_t index) {
// Precondition - an entry for index must exist in the node
Node *&getChildExists(Node3 *self, uint8_t index) {
return self->children[getNodeIndex(self, index)];
auto &result = self->children[getNodeIndex(self, index)];
simCacheMiss(result);
return result;
}
// Precondition - an entry for index must exist in the node
Node *&getChildExists(Node16 *self, uint8_t index) {
return self->children[getNodeIndex(self, index)];
auto &result = self->children[getNodeIndex(self, index)];
simCacheMiss(result);
return result;
}
// Precondition - an entry for index must exist in the node
Node *&getChildExists(Node48 *self, uint8_t index) {
assert(self->bitSet.test(index));
return self->children[self->index[index]];
auto &result = self->children[self->index[index]];
simCacheMiss(result);
return result;
}
// Precondition - an entry for index must exist in the node
Node *&getChildExists(Node256 *self, uint8_t index) {
assert(self->bitSet.test(index));
return self->children[index];
auto &result = self->children[index];
simCacheMiss(result);
return result;
}
// Precondition - an entry for index must exist in the node
@@ -1030,6 +1049,7 @@ ChildAndMaxVersion getChildAndMaxVersion(Node3 *self, uint8_t index) {
if (i < 0) {
return {};
}
simCacheMiss(self->children[i]);
return {self->children[i], self->childMaxVersion[i]};
}
ChildAndMaxVersion getChildAndMaxVersion(Node16 *self, uint8_t index) {
@@ -1037,6 +1057,7 @@ ChildAndMaxVersion getChildAndMaxVersion(Node16 *self, uint8_t index) {
if (i < 0) {
return {};
}
simCacheMiss(self->children[i]);
return {self->children[i], self->childMaxVersion[i]};
}
ChildAndMaxVersion getChildAndMaxVersion(Node48 *self, uint8_t index) {
@@ -1044,9 +1065,11 @@ ChildAndMaxVersion getChildAndMaxVersion(Node48 *self, uint8_t index) {
if (i < 0) {
return {};
}
simCacheMiss(self->children[i]);
return {self->children[i], self->childMaxVersion[i]};
}
ChildAndMaxVersion getChildAndMaxVersion(Node256 *self, uint8_t index) {
simCacheMiss(self->children[index]);
return {self->children[index], self->childMaxVersion[index]};
}
@@ -1072,6 +1095,7 @@ Node *getChildGeq(Node0 *, int) { return nullptr; }
Node *getChildGeq(Node3 *n, int child) {
for (int i = 0; i < n->numChildren; ++i) {
if (n->index[i] >= child) {
simCacheMiss(n->children[i]);
return n->children[i];
}
}
@@ -1090,7 +1114,10 @@ Node *getChildGeq(Node16 *self, int child) {
__m128i results = _mm_cmpeq_epi8(key_vec, _mm_min_epu8(key_vec, indices));
int mask = (1 << self->numChildren) - 1;
uint32_t bitfield = _mm_movemask_epi8(results) & mask;
return bitfield == 0 ? nullptr : self->children[std::countr_zero(bitfield)];
auto *result =
bitfield == 0 ? nullptr : self->children[std::countr_zero(bitfield)];
simCacheMiss(result);
return result;
#elif defined(HAS_ARM_NEON)
uint8x16_t indices;
memcpy(&indices, self->index, sizeof(self->index));
@@ -1126,13 +1153,16 @@ Node *getChildGeq(Node48 *self, int child) {
if (c < 0) {
return nullptr;
}
return self->children[self->index[c]];
auto *result = self->children[self->index[c]];
simCacheMiss(result);
return result;
}
Node *getChildGeq(Node256 *self, int child) {
int c = self->bitSet.firstSetGeq(child);
if (c < 0) {
return nullptr;
}
simCacheMiss(self->children[c]);
return self->children[c];
}
@@ -1156,20 +1186,26 @@ Node *getChildGeq(Node *self, int child) {
// Precondition: self has a child
Node *getFirstChildExists(Node3 *self) {
assert(self->numChildren > 0);
simCacheMiss(self->children[0]);
return self->children[0];
}
// Precondition: self has a child
Node *getFirstChildExists(Node16 *self) {
assert(self->numChildren > 0);
simCacheMiss(self->children[0]);
return self->children[0];
}
// Precondition: self has a child
Node *getFirstChildExists(Node48 *self) {
return self->children[self->index[self->bitSet.firstSetGeq(0)]];
auto *result = self->children[self->index[self->bitSet.firstSetGeq(0)]];
simCacheMiss(result);
return result;
}
// Precondition: self has a child
Node *getFirstChildExists(Node256 *self) {
return self->children[self->bitSet.firstSetGeq(0)];
auto *result = self->children[self->bitSet.firstSetGeq(0)];
simCacheMiss(result);
return result;
}
// Precondition: self has a child
@@ -3010,18 +3046,10 @@ Node *firstGeqPhysical(Node *n, const std::span<const uint8_t> key) {
}
struct CheckJob {
Node *n;
std::span<const uint8_t> begin;
InternalVersionT readVersion;
ReadContext *tls;
ConflictSet::Result *result;
void setResult(bool ok) {
*result = ok ? ConflictSet::Commit : ConflictSet::Conflict;
}
typedef void (*typeErasedContinuation)(void *);
// The type of a function that takes a CheckJob* and returns its own type
struct continuation {
typedef continuation (*functionPtrType)(CheckJob *);
@@ -3032,9 +3060,16 @@ struct CheckJob {
operator bool() { return func != nullptr; }
};
continuation next;
void init(const ConflictSet::ReadRange *read, ConflictSet::Result *result,
Node *root, int64_t oldestVersionFullPrecision, ReadContext *tls);
continuation next;
Node *n;
ChildAndMaxVersion childAndVersion;
std::span<const uint8_t> begin;
InternalVersionT readVersion;
ReadContext *tls;
ConflictSet::Result *result;
};
namespace check_point_read_state_machine {
@@ -3042,18 +3077,12 @@ namespace check_point_read_state_machine {
CheckJob::continuation down_left_spine(CheckJob *job);
CheckJob::continuation iter(CheckJob *job);
// Logically this is the same as performing firstGeq and then checking against
// point or range version according to cmp, but this version short circuits as
// soon as it can prove that there's no conflict.
CheckJob::continuation begin(CheckJob *job) {
++job->tls->point_read_accum;
#if DEBUG_VERBOSE && !defined(NDEBUG)
fprintf(stderr, "Check point read: %s\n", printable(key).c_str());
#endif
return iter(job);
}
CheckJob::continuation iter(CheckJob *job) {
if (job->begin.size() == 0) {
if (job->n->entryPresent) {
job->setResult(job->n->entry.pointVersion <= job->readVersion);
@@ -3063,11 +3092,17 @@ CheckJob::continuation iter(CheckJob *job) {
return down_left_spine;
}
auto [child, maxV] = getChildAndMaxVersion(job->n, job->begin[0]);
if (child == nullptr) {
job->childAndVersion = getChildAndMaxVersion(job->n, job->begin[0]);
__builtin_prefetch(job->childAndVersion.child);
return iter;
}
CheckJob::continuation iter(CheckJob *job) {
if (job->childAndVersion.child == nullptr) {
auto c = getChildGeq(job->n, job->begin[0]);
if (c != nullptr) {
job->n = c;
__builtin_prefetch(job->n);
return down_left_spine;
} else {
job->n = nextSibling(job->n);
@@ -3075,11 +3110,12 @@ CheckJob::continuation iter(CheckJob *job) {
job->setResult(true);
return nullptr; // Done
}
__builtin_prefetch(job->n);
return down_left_spine;
}
}
job->n = child;
job->n = job->childAndVersion.child;
job->begin = job->begin.subspan(1, job->begin.size() - 1);
if (job->n->partialKeyLen > 0) {
@@ -3089,13 +3125,14 @@ CheckJob::continuation iter(CheckJob *job) {
if (i < commonLen) {
auto c = job->n->partialKey()[i] <=> job->begin[i];
if (c > 0) {
return down_left_spine;
return down_left_spine(job);
} else {
job->n = nextSibling(job->n);
if (job->n == nullptr) {
job->setResult(true);
return nullptr; // Done
}
__builtin_prefetch(job->n);
return down_left_spine;
}
}
@@ -3105,17 +3142,30 @@ CheckJob::continuation iter(CheckJob *job) {
} else if (job->n->partialKeyLen > int(job->begin.size())) {
// n is the first physical node greater than remaining, and there's no
// eq node
return down_left_spine;
return down_left_spine(job);
}
}
if (maxV <= job->readVersion) {
if (job->childAndVersion.maxVersion <= job->readVersion) {
++job->tls->point_read_short_circuit_accum;
job->setResult(true);
return nullptr; // Done
}
++job->tls->point_read_iterations_accum;
if (job->begin.size() == 0) {
if (job->n->entryPresent) {
job->setResult(job->n->entry.pointVersion <= job->readVersion);
return nullptr; // Done
}
job->n = getFirstChildExists(job->n);
__builtin_prefetch(job->n);
return down_left_spine;
}
job->childAndVersion = getChildAndMaxVersion(job->n, job->begin[0]);
__builtin_prefetch(job->childAndVersion.child);
return iter;
}
@@ -3125,6 +3175,7 @@ CheckJob::continuation down_left_spine(CheckJob *job) {
return nullptr; // Done
}
job->n = getFirstChildExists(job->n);
__builtin_prefetch(job->n);
return down_left_spine;
}
@@ -3145,6 +3196,11 @@ void CheckJob::init(const ConflictSet::ReadRange *read,
this->result = result;
this->tls = tls;
this->next = check_point_read_state_machine::begin;
// *result =
// checkPointRead(root, begin, InternalVersionT(read->readVersion), tls)
// ? ConflictSet::Commit
// : ConflictSet::Conflict;
// next = +[](CheckJob *) -> continuation { return nullptr; };
} else {
*result = checkRangeRead(root, begin, end,
InternalVersionT(read->readVersion), tls)