From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Sat, 9 May 2020 14:04:17 +0000 (+0100)
Subject: Performance: workaround Linux kernel bug
X-Git-Tag: exim-4.94-RC1~4
X-Git-Url: https://git.exim.org/exim.git/commitdiff_plain/68f71b94cc10f8b0453597d0f92b4bd7d995eeef

Performance: workaround Linux kernel bug
---

diff --git a/src/src/smtp_out.c b/src/src/smtp_out.c
index 6f7fb85c1..86c3e4127 100644
--- a/src/src/smtp_out.c
+++ b/src/src/smtp_out.c
@@ -509,6 +509,16 @@ else
 	      0
 #endif
 	     );
+
+#if defined(__linux__)
+    /* This is a workaround for a current linux kernel bug: as of
+    5.6.8-200.fc31.x86_64  small (<MSS) writes get delayed by about 200ms,
+    This is despite NODELAY being active.
+    https://bugzilla.redhat.com/show_bug.cgi?id=1803806 */
+
+    if (!more)
+      setsockopt(outblock->cctx->sock, IPPROTO_TCP, TCP_CORK, &off, sizeof(off));
+#endif
     }
   }