Re: [PATCH] CI: add SANITIZE=[address|undefined] jobs

[Jeff King <peff@peff.net>]

On Thu, Jul 28, 2022 at 05:09:38PM -0400, Jeff King wrote:

> > Ditto TEST_NO_MALLOC_CHECK=1 & --no-bin-wrappers, but we can think about
> > all of those some other time....
> 
> I'd be surprised if the malloc checking itself is all that expensive,
> though it does look like we call getconf and expr once per test there
> for setup. We could almost certainly hoist that out and call it once per
> script.

Nope, I was totally wrong here. Running with TEST_NO_MALLOC_CHECK=1 does
indeed make a big difference:

  Benchmark 1: make test
    Time (mean ± σ):     67.486 s ±  3.339 s    [User: 622.643 s, System: 409.951 s]
    Range (min … max):   63.634 s … 69.550 s    3 runs
   
  Benchmark 2: TEST_NO_MALLOC_CHECK=1 make test
    Time (mean ± σ):     57.596 s ±  0.899 s    [User: 577.273 s, System: 291.627 s]
    Range (min … max):   57.072 s … 58.634 s    3 runs

Eliminating the extra per-test processes with the patch below helps a
little, but most of the effort really is (presumably) going to the
actual malloc checking code:

  Benchmark 1: make test [nb: after applying patch...]
  Time (mean ± σ):     67.091 s ±  0.385 s    [User: 599.382 s, System: 410.781 s]
  Range (min … max):   66.648 s … 67.343 s    3 runs

Curious that most of the CPU time seems to go into system time. I'd have
thought it was extra internal malloc debugging bits, but maybe it is
allocating mmap/brk calls in a less efficient way. I dunno how any of it
actually works.

-Peff

---
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 55857af601..303fbe8ecc 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -557,14 +557,20 @@ then
 		: nothing
 	}
 else
+	if _GLIBC_VERSION=$(getconf GNU_LIBC_VERSION 2>/dev/null) &&
+	   _GLIBC_VERSION=${_GLIBC_VERSION#"glibc "} &&
+	    expr 2.34 \<= "$_GLIBC_VERSION" >/dev/null
+	then
+		USE_LIBC_MALLOC_DEBUG=t
+	else
+		USE_LIBC_MALLOC_DEBUG=
+	fi
 	setup_malloc_check () {
 		local g
 		local t
 		MALLOC_CHECK_=3	MALLOC_PERTURB_=165
 		export MALLOC_CHECK_ MALLOC_PERTURB_
-		if _GLIBC_VERSION=$(getconf GNU_LIBC_VERSION 2>/dev/null) &&
-		   _GLIBC_VERSION=${_GLIBC_VERSION#"glibc "} &&
-		   expr 2.34 \<= "$_GLIBC_VERSION" >/dev/null
+		if test -n "$USE_LIBC_MALLOC_DEBUG"
 		then
 			g=
 			LD_PRELOAD="libc_malloc_debug.so.0"