Manually lay out scorer memory

[rust-lightning] / lightning / src / routing / scoring.rs

diff --git a/lightning/src/routing/scoring.rs b/lightning/src/routing/scoring.rs
index 42a565aee95b908b4a60ddf6c99b10ba98899987..cde615b9f10578d789826a1e480c0c44ce143eba 100644 (file)
--- a/lightning/src/routing/scoring.rs
+++ b/lightning/src/routing/scoring.rs
@@ -780,6 +780,7 @@ impl ProbabilisticScoringDecayParameters {
 /// Direction is defined in terms of [`NodeId`] partial ordering, where the source node is the
 /// first node in the ordering of the channel's counterparties. Thus, swapping the two liquidity
 /// offset fields gives the opposite direction.
+#[repr(C)] // Force the fields in memory to be in the order we specify
 struct ChannelLiquidity {
        /// Lower channel liquidity bound in terms of an offset from zero.
        min_liquidity_offset_msat: u64,
@@ -797,6 +798,16 @@ struct ChannelLiquidity {
        offset_history_last_updated: Duration,
 }
 
+// Check that the liquidity HashMap's entries sit on round cache lines.
+//
+// Specifically, the first cache line will have the key, the liquidity offsets, and the total
+// points tracked in the historical tracker.
+//
+// The next two cache lines will have the historical points, which we only access last during
+// scoring, followed by the last_updated `Duration`s (which we do not need during scoring).
+const _LIQUIDITY_MAP_SIZING_CHECK: usize = 192 - ::core::mem::size_of::<(u64, ChannelLiquidity)>();
+const _LIQUIDITY_MAP_SIZING_CHECK_2: usize = ::core::mem::size_of::<(u64, ChannelLiquidity)>() - 192;
+
 /// A snapshot of [`ChannelLiquidity`] in one direction assuming a certain channel capacity and
 /// decayed with a given half life.
 struct DirectedChannelLiquidity<L: Deref<Target = u64>, HT: Deref<Target = HistoricalLiquidityTracker>, T: Deref<Target = Duration>> {
@@ -1487,10 +1498,24 @@ mod bucketed_history {
        // between the 12,000th sat and 24,000th sat, while only needing to store and operate on 32
        // buckets in total.
 
-       const BUCKET_START_POS: [u16; 33] = [
-               0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 3072, 4096, 6144, 8192, 10240, 12288,
-               13312, 14336, 15360, 15872, 16128, 16256, 16320, 16352, 16368, 16376, 16380, 16382, 16383, 16384,
-       ];
+       // By default u16s may not be cache-aligned, but we'd rather not have to read a third cache
+       // line just to access it
+       #[repr(align(128))]
+       struct BucketStartPos([u16; 33]);
+       impl BucketStartPos {
+               const fn new() -> Self {
+                       Self([
+                               0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 3072, 4096, 6144, 8192, 10240, 12288,
+                               13312, 14336, 15360, 15872, 16128, 16256, 16320, 16352, 16368, 16376, 16380, 16382, 16383, 16384,
+                       ])
+               }
+       }
+       impl core::ops::Index<usize> for BucketStartPos {
+               type Output = u16;
+               #[inline(always)]
+               fn index(&self, index: usize) -> &u16 { &self.0[index] }
+       }
+       const BUCKET_START_POS: BucketStartPos = BucketStartPos::new();
 
        const LEGACY_TO_BUCKET_RANGE: [(u8, u8); 8] = [
                (0, 12), (12, 14), (14, 15), (15, 16), (16, 17), (17, 18), (18, 20), (20, 32)
@@ -1628,10 +1653,11 @@ mod bucketed_history {
        impl_writeable_tlv_based!(LegacyHistoricalBucketRangeTracker, { (0, buckets, required) });
 
        #[derive(Clone, Copy)]
+       #[repr(C)] // Force the fields in memory to be in the order we specify.
        pub(super) struct HistoricalLiquidityTracker {
+               total_valid_points_tracked: u64,
                min_liquidity_offset_history: HistoricalBucketRangeTracker,
                max_liquidity_offset_history: HistoricalBucketRangeTracker,
-               total_valid_points_tracked: u64,
        }
 
        impl HistoricalLiquidityTracker {