[Ur] Drop of several orders of magnitude in Techempower benchmarks

[Benjamin Barenblat]

On Monday, August  5, 2019, at 10:17 PM +01, Oisín Mac Fhearaí wrote:
> I was able to [...] update the Dockerfile to build Ur/web from the
> latest release tarball [...] and compare the benchmarks with the version
> installed with apt from the Ubuntu repo. The version built from the
> latest release was over ten times faster, even running on my old laptop.

On Tuesday, August  6, 2019, at  1:59 PM -04, Adam Chlipala wrote:
> I've asked the Debian packager if he can think of some build-process
> change there that would have introduced a slowdown.

Hi, Debian packager here. Sorry for the latency of this reply – I hope
nobody’s been racking their brain trying to figure this one out.

This is in fact an issue with the Debian packaging. In particular,
upstream Ur/Web builds the runtime with -U_FORTIFY_SOURCE, but Debian
builds it with -D_FORTIFY_SOURCE=2. This causes a truly impressive
slowdown, as you can read about in https://bugs.debian.org/934722. I’m
going to do a bit more digging to see if I can understand the issue
further, but I expect I’ll just end up downgrading the Debian package to
-D_FORTIFY_SOURCE=1. I expect this has no performance impact, but Oisín,
if you want to check me, you can patch Ur/Web master with

--8<-----------------cut here------------------start--------------->8---
diff --git a/src/c/Makefile.am b/src/c/Makefile.am
index 95582793..ad8cbd3e 100644
--- a/src/c/Makefile.am
+++ b/src/c/Makefile.am
@@ -7,7 +7,7 @@ liburweb_fastcgi_la_SOURCES = fastcgi.c fastcgi.h
 liburweb_static_la_SOURCES = static.c
 
 AM_CPPFLAGS = -I$(srcdir)/../../include/urweb $(OPENSSL_INCLUDES) $(ICU_INCLUDES)
-AM_CFLAGS = -Wall -Wunused-parameter -Werror -Wno-format-security -Wno-deprecated-declarations -U_FORTIFY_SOURCE $(PTHREAD_CFLAGS)
+AM_CFLAGS = -Wall -Wunused-parameter -Werror -Wno-format-security -Wno-deprecated-declarations -D_FORTIFY_SOURCE=1 $(PTHREAD_CFLAGS)
 liburweb_la_LDFLAGS = $(AM_LDFLAGS) $(OPENSSL_LDFLAGS) \
        -export-symbols-regex '^(client_pruner|pthread_create_big|strcmp_nullsafe|uw_.*)' \
        -version-info 1:0:0
--8<-----------------cut here------------------end----------------->8---

and give the benchmarks another shot.