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perf: Raise the sweep worker cap to 8

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A cap of 4 measured slower than the uncapped sweep on 8-core hosts, so
raise the cap to 8 and take the question of the right value to review.

Trim the sweep comments to the fact and its consequence.
This commit is contained in:
Pratik Mankawde
2026-09-21 13:32:47 +01:00
parent f5900b96e8
commit 5429595fb9
3 changed files with 14 additions and 21 deletions
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25
include/xrpl/basics/TaggedCache.h
View File

@@ -75,12 +75,10 @@ public:
/**
* Most worker threads a single sweep() may start.
*
* The cache is split into partitions and sweep() shares them out over its
* workers. A worker takes several partitions when there are more of them
* than this, so the thread count is fixed however many partitions the
* cache holds and however many cores the host has.
* A worker takes several partitions when there are more than this, so the
* thread count does not follow the host's core count.
*/
static constexpr std::size_t kMaxSweepThreads = 4;
static constexpr std::size_t kMaxSweepThreads = 8;
public:
TaggedCache(
@@ -370,12 +368,11 @@ private:
* Sweeps one partition of a key/value cache, in the calling thread.
*
* @param whenExpire Entries last accessed at or before this point expire.
* @param now Current time, used to pull back a timestamp set in the future.
* @param now Current time, used to pull back a future timestamp.
* @param partition The one partition to walk.
* @param stuffToSweep Collects the evicted pointers so the caller can
* destroy them once it has released the cache lock.
* @param allRemovals Accumulates this partition's removal count across all
* workers.
* @param stuffToSweep Collects evicted pointers, destroyed once the caller
* releases the cache lock.
* @param allRemovals Accumulates removals across all workers.
*/
void
sweepPartition(
@@ -389,14 +386,12 @@ private:
/**
* Sweeps one partition of a key-only cache, in the calling thread.
*
* A key-only cache owns no pointers, so nothing is collected for later
* destruction and the stuffToSweep parameter is unused.
* A key-only cache owns no pointers, so stuffToSweep is unused.
*
* @param whenExpire Entries last accessed at or before this point expire.
* @param now Current time, used to pull back a timestamp set in the future.
* @param now Current time, used to pull back a future timestamp.
* @param partition The one partition to walk.
* @param allRemovals Accumulates this partition's removal count across all
* workers.
* @param allRemovals Accumulates removals across all workers.
*/
void
sweepPartition(

6
include/xrpl/basics/TaggedCache.ipp
View File

@@ -262,10 +262,8 @@ TaggedCache<Key, T, IsKeyCache, SharedWeakUnionPointer, SharedPointerType, Hash,
<< " aging at " << (now - whenExpire).count() << " of " << targetAge_.count();
}
// Share the partitions out over a fixed number of workers, so the
// thread count does not follow the partition count. Worker w takes
// partitions w, w + workerCount, w + 2 * workerCount and so on, which
// covers every partition exactly once.
// Worker w takes partitions w, w + workerCount, w + 2 * workerCount
// and so on, covering every partition exactly once.
std::size_t const workerCount = std::min(cache_.partitions(), kMaxSweepThreads);
std::vector<std::thread> workers;

4
src/tests/libxrpl/basics/TaggedCache.cpp
View File

@@ -248,9 +248,9 @@ TEST(TaggedCacheTest, sweep_thread_count_is_capped)
{
using Cache = TaggedCache<LedgerIndex, std::string>;
// sweep() runs one worker per partition unless it is capped, and the
// Without the cap, sweep() runs one worker per partition, and the
// partition count follows the host's core count.
EXPECT_EQ(Cache::kMaxSweepThreads, 4u);
EXPECT_EQ(Cache::kMaxSweepThreads, 8u);
}
TEST(TaggedCacheTest, sweep_evicts_from_every_partition)