head-revs: add a native implementation of the `stop_rev` parameter This does not add too much complexity to the native code and help with branchmap v3 performance. Note that the final conversion of the heads from native-code to Python is still too costly, especially in Rust. In addition the current caching around headrevs is too simple and fragile. However these are an unrelated problem. ### benchmark.name = hg.command.unbundle # bin-env-vars.hg.py-re2-module = default # benchmark.variants.issue6528 = disabled # benchmark.variants.resource-usage = default # benchmark.variants.reuse-external-delta-parent = yes # benchmark.variants.revs = any-1-extra-rev # benchmark.variants.source = unbundle # benchmark.variants.validate = default # benchmark.variants.verbosity = quiet ## data-env-vars.name = netbeans-2018-08-01-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 0.233711 ~~~~~ branch-v3 before: 0.239857 (+2.63%, +0.01) branch-v3 after: 0.239558 (+2.50%, +0.01) # bin-env-vars.hg.flavor = rust branch-v2: 0.235230 ~~~~~ branch-v3 before: 0.240972 (+2.44%, +0.01) branch-v3 after: 0.239917 (+1.99%, +0.00) ## data-env-vars.name = netbeans-2018-08-01-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 0.255586 ~~~~~ branch-v3 before: 0.268560 (+5.08%, +0.01) branch-v3 after: 0.262261 (+2.61%, +0.01) ## data-env-vars.name = mozilla-central-2024-03-22-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 0.339010 ~~~~~ branch-v3 before: 0.349389 (+3.06%, +0.01) branch-v3 after: 0.348247 (+2.72%, +0.01) # bin-env-vars.hg.flavor = rust branch-v2: 0.346525 ~~~~~ branch-v3 before: 0.355661 (+2.64%, +0.01) branch-v3 after: 0.350906 (+1.26%, +0.00) ## data-env-vars.name = mozilla-central-2024-03-22-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 0.380202 ~~~~~ branch-v3 before: 0.408851 (+7.54%, +0.03) branch-v3 after: 0.406511 (+6.92%, +0.03) ## data-env-vars.name = mozilla-unified-2024-03-22-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 0.412165 ~~~~~ branch-v3 before: 0.427782 (+3.79%, +0.02) branch-v3 after: 0.422595 (+2.53%, +0.01) # bin-env-vars.hg.flavor = rust branch-v2: 0.412397 ~~~~~ branch-v3 before: 0.422354 (+2.41%, +0.01) branch-v3 after: 0.421079 (+2.11%, +0.01) ## data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 0.429501 ~~~~~ branch-v3 before: 0.443197 (+3.19%, +0.01) branch-v3 after: 0.449432 (+4.64%, +0.02) ## data-env-vars.name = mozilla-try-2024-03-26-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 3.403171 ~~~~~ branch-v3 before: 3.819477 (+12.23%, +0.42) branch-v3 after: 3.658482 (+7.50%, +0.26) # bin-env-vars.hg.flavor = rust branch-v2: 3.454876 ~~~~~ branch-v3 before: 3.590284 (+3.92%, +0.14) branch-v3 after: 3.545843 (+2.63%, +0.09) ## data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 3.465435 ~~~~~ branch-v3 before: 3.633278 (+4.84%, +0.17) branch-v3 after: 3.556074 (+2.62%, +0.09)

--- a/mercurial/pure/parsers.py	Thu Sep 26 01:52:09 2024 +0200
+++ b/mercurial/pure/parsers.py	Fri Sep 27 03:55:40 2024 +0200
@@ -696,8 +696,10 @@
             p = p[revlog_constants.INDEX_HEADER.size :]
         return p
 
-    def headrevs(self, excluded_revs=None):
+    def headrevs(self, excluded_revs=None, stop_rev=None):
         count = len(self)
+        if stop_rev is not None:
+            count = min(count, stop_rev)
         if not count:
             return [nullrev]
         # we won't iter over filtered rev so nobody is a head at start