Align `PathBuildingHop` to 128b, now that we store them in a `Vec`

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

diff --git a/lightning/src/routing/router.rs b/lightning/src/routing/router.rs
index 28270baa1f57fa00c9298b652c77d8dff220ca18..a8c8e133034590ccee65ef9e3491c3d5009456cd 100644 (file)
--- a/lightning/src/routing/router.rs
+++ b/lightning/src/routing/router.rs
@@ -1111,12 +1111,7 @@ impl cmp::PartialOrd for RouteGraphNode {
 
 // While RouteGraphNode can be laid out with fewer bytes, performance appears to be improved
 // substantially when it is laid out at exactly 64 bytes.
-//
-// Thus, we use `#[repr(C)]` on the struct to force a suboptimal layout and check that it stays 64
-// bytes here.
-#[cfg(any(ldk_bench, not(any(test, fuzzing))))]
 const _GRAPH_NODE_SMALL: usize = 64 - core::mem::size_of::<RouteGraphNode>();
-#[cfg(any(ldk_bench, not(any(test, fuzzing))))]
 const _GRAPH_NODE_FIXED_SIZE: usize = core::mem::size_of::<RouteGraphNode>() - 64;
 
 /// A [`CandidateRouteHop::FirstHop`] entry.
@@ -1491,7 +1486,7 @@ fn iter_equal<I1: Iterator, I2: Iterator>(mut iter_a: I1, mut iter_b: I2)
 /// Fee values should be updated only in the context of the whole path, see update_value_and_recompute_fees.
 /// These fee values are useful to choose hops as we traverse the graph "payee-to-payer".
 #[derive(Clone)]
-#[repr(C)] // Force fields to appear in the order we define them.
+#[repr(align(128))]
 struct PathBuildingHop<'a> {
        candidate: CandidateRouteHop<'a>,
        target_node_counter: Option<u32>,
@@ -1521,11 +1516,6 @@ struct PathBuildingHop<'a> {
        /// channel scoring.
        path_penalty_msat: u64,
 
-       // The last 16 bytes are on the next cache line by default in glibc's malloc. Thus, we should
-       // only place fields which are not hot there. Luckily, the next three fields are only read if
-       // we end up on the selected path, and only in the final path layout phase, so we don't care
-       // too much if reading them is slow.
-
        fee_msat: u64,
 
        /// All the fees paid *after* this channel on the way to the destination
@@ -1542,17 +1532,8 @@ struct PathBuildingHop<'a> {
        value_contribution_msat: u64,
 }
 
-// Checks that the entries in the `find_route` `dist` map fit in (exactly) two standard x86-64
-// cache lines. Sadly, they're not guaranteed to actually lie on a cache line (and in fact,
-// generally won't, because at least glibc's malloc will align to a nice, big, round
-// boundary...plus 16), but at least it will reduce the amount of data we'll need to load.
-//
-// Note that these assertions only pass on somewhat recent rustc, and thus are gated on the
-// ldk_bench flag.
-#[cfg(ldk_bench)]
-const _NODE_MAP_SIZE_TWO_CACHE_LINES: usize = 128 - core::mem::size_of::<(NodeId, PathBuildingHop)>();
-#[cfg(ldk_bench)]
-const _NODE_MAP_SIZE_EXACTLY_CACHE_LINES: usize = core::mem::size_of::<(NodeId, PathBuildingHop)>() - 128;
+const _NODE_MAP_SIZE_TWO_CACHE_LINES: usize = 128 - core::mem::size_of::<Option<PathBuildingHop>>();
+const _NODE_MAP_SIZE_EXACTLY_TWO_CACHE_LINES: usize = core::mem::size_of::<Option<PathBuildingHop>>() - 128;
 
 impl<'a> core::fmt::Debug for PathBuildingHop<'a> {
        fn fmt(&self, f: &mut core::fmt::Formatter) -> Result<(), core::fmt::Error> {