dnsdist on s390x: check shard->respRing.size() > entriesPerShard * 0.95 has failed

[zeha]

• Program: dnsdist 1.3.0
• Issue type: Bug report

On Debian s390x, the tests fail with:

test-dnsdistrings_cc.cc(243): error: in "dnsdistrings_cc/test_Rings_Threaded": check shard->respRing.size() > entriesPerShard * 0.95 has failed [18924 <= 19000]

Havent looked myself what this means yet.

[rgacogne]

It means that the shard distribution was not really uniform, probably because the contention was a lot worse than expected. I'll turn that into a warning since it only matters when the corresponding code has been altered.

[zeha]

i'll be testing this on the buildds:

diff --git a/pdns/dnsdistdist/test-dnsdistrings_cc.cc b/pdns/dnsdistdist/test-dnsdistrings_cc.cc
index c98016c72..8e76e0836 100644
--- a/pdns/dnsdistdist/test-dnsdistrings_cc.cc
+++ b/pdns/dnsdistdist/test-dnsdistrings_cc.cc
@@ -230,7 +230,10 @@ BOOST_AUTO_TEST_CASE(test_Rings_Threaded) {
   size_t totalResponses = 0;
   for (const auto& shard : rings.d_shards) {
     BOOST_CHECK_LE(shard->queryRing.size(), entriesPerShard);
-    BOOST_CHECK_GT(shard->queryRing.size(), entriesPerShard * 0.95);
+    // verify that the shard is not empty
+    BOOST_CHECK_GT(shard->queryRing.size(), (entriesPerShard * 0.5) + 1);
+    // this would be optimal
+    BOOST_WARN_GT(shard->queryRing.size(), entriesPerShard * 0.95);
     totalQueries += shard->queryRing.size();
     for (const auto& entry : shard->queryRing) {
       BOOST_CHECK_EQUAL(entry.name, qname);
@@ -240,7 +243,10 @@ BOOST_AUTO_TEST_CASE(test_Rings_Threaded) {
       BOOST_CHECK_EQUAL(entry.requestor.toStringWithPort(), requestor.toStringWithPort());
     }
     BOOST_CHECK_LE(shard->respRing.size(), entriesPerShard);
-    BOOST_CHECK_GT(shard->respRing.size(), entriesPerShard * 0.95);
+    // verify that the shard is not empty
+    BOOST_CHECK_GT(shard->queryRing.size(), (entriesPerShard * 0.5) + 1);
+    // this would be optimal
+    BOOST_WARN_GT(shard->respRing.size(), entriesPerShard * 0.95);
     totalResponses += shard->respRing.size();
     for (const auto& entry : shard->respRing) {
       BOOST_CHECK_EQUAL(entry.name, qname);

[zeha]

Needs more on s390x, current diff:
master...zeha:dnsdist-shard-test

Not sure why this is only a problem on s390x.

[Habbie]

Not sure why this is only a problem on s390x.

I just saw it happen in Travis.