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Make binary search faster with 11 parallel queries

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This commit is contained in:
Quentin McGaw
2025-09-10 15:52:04 +00:00
parent 162d244865
commit d83999d954
2 changed files with 12 additions and 10 deletions
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14
internal/pmtud/pmtud.go
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@@ -132,18 +132,17 @@ func pmtudMultiSizes(ctx context.Context, ip netip.Addr,
// cannot be working if we had a timeout.
for i := len(tests) - 2; i >= 0; i-- { //nolint:mnd
if tests[i].ok {
return pmtudMultiSizes(ctx, ip, tests[i].mtu, tests[i+1].mtu,
return pmtudMultiSizes(ctx, ip, tests[i].mtu, tests[i+1].mtu-1,
pingTimeout, logger)
}
}
// All MTUs failed.
if tests[0].mtu == minMTU+1 {
if tests[0].mtu == minMTU+1 { // All MTUs failed.
return minMTU, nil
}
// Re-test with MTUs between the minimum MTU
// and the smallest next MTU we tested.
return pmtudMultiSizes(ctx, ip, minMTU, tests[0].mtu,
return pmtudMultiSizes(ctx, ip, minMTU, tests[0].mtu-1,
pingTimeout, logger)
case err != nil:
return 0, fmt.Errorf("collecting ICMP echo replies: %w", err)
@@ -152,14 +151,17 @@ func pmtudMultiSizes(ctx context.Context, ip netip.Addr,
}
}
// Create the MTU slice of length 8 such that:
// Create the MTU slice of length 11 such that:
// - the first element is the minMTU plus the step
// - the last element is the maxMTU
// - elements in-between are separated as close to each other
// - Don't make the minMTU part of the MTUs to test since
// it's assumed it's already working.
// The number 11 is chosen to find the final MTU in 3 searches;
// to find it in 2 searches requires 37 parallel queries which
// could be blocked by firewalls.
func makeMTUsToTest(minMTU, maxMTU int) (mtus []int) {
const mtusLength = 8
const mtusLength = 11 // find the final MTU in 3 searches
diff := maxMTU - minMTU
switch {
case minMTU > maxMTU: