Re: [PATCH for 5.1 3/3] rseq/selftests: Adapt number of threads to the number of detected cpus

----- On Apr 19, 2019, at 9:42 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

----- On Apr 19, 2019, at 8:55 AM, Mathieu Desnoyers
mathieu.desnoyers@efficios.com wrote:

quoted

----- On Apr 19, 2019, at 8:41 AM, Mathieu Desnoyers
mathieu.desnoyers@efficios.com wrote:

quoted

----- On Apr 19, 2019, at 6:38 AM, Ingo Molnar mingo@kernel.org wrote:

quoted

* Mathieu Desnoyers [off-list ref] wrote:

quoted

On smaller systems, running a test with 200 threads can take a long
time on machines with smaller number of CPUs.

Detect the number of online cpus at test runtime, and multiply that
by 6 to have 6 rseq threads per cpu preempting each other.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Gleixner <redacted>
Cc: Joel Fernandes <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Watson <redacted>
Cc: Will Deacon <redacted>
Cc: Andi Kleen <redacted>
Cc: linux-kselftest@vger.kernel.org
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Chris Lameter <redacted>
Cc: Russell King <redacted>
Cc: Michael Kerrisk <redacted>
Cc: "Paul E . McKenney" <redacted>
Cc: Paul Turner <redacted>
Cc: Boqun Feng <redacted>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Maurer <redacted>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
---
 tools/testing/selftests/rseq/run_param_test.sh | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/run_param_test.sh

b/tools/testing/selftests/rseq/run_param_test.sh
index 3acd6d75ff9f..e426304fd4a0 100755

--- a/tools/testing/selftests/rseq/run_param_test.sh
+++ b/tools/testing/selftests/rseq/run_param_test.sh

@@ -1,6 +1,8 @@
 #!/bin/bash
 # SPDX-License-Identifier: GPL-2.0+ or MIT
 
+NR_CPUS=`grep '^processor' /proc/cpuinfo | wc -l`
+
 EXTRA_ARGS=${@}
 
 OLDIFS="$IFS"

@@ -28,15 +30,16 @@ IFS="$OLDIFS"
 
 REPS=1000
 SLOW_REPS=100
+NR_THREADS=$((6*${NR_CPUS}))
 
 function do_tests()
 {
 	local i=0
 	while [ "$i" -lt "${#TEST_LIST[@]}" ]; do
 		echo "Running test ${TEST_NAME[$i]}"
-		./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+		./param_test ${TEST_LIST[$i]} -r ${REPS} -t ${NR_THREADS} ${@} ${EXTRA_ARGS}

|| exit 1
 		echo "Running compare-twice test ${TEST_NAME[$i]}"
-		./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} ||
exit 1
+		./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} -t ${NR_THREADS} ${@}
${EXTRA_ARGS} || exit 1
 		let "i++"
 	done
 }

BTW., when trying to build the rseq self-tests I get this build failure:

 dagon:~/tip/tools/testing/selftests/rseq> make
 gcc -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./ -shared
 -fPIC rseq.c -lpthread -o
 /home/mingo/tip/tools/testing/selftests/rseq/librseq.so
 gcc -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./ basic_test.c
 -lpthread -lrseq -o /home/mingo/tip/tools/testing/selftests/rseq/basic_test
 gcc -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./
 basic_percpu_ops_test.c -lpthread -lrseq -o
 /home/mingo/tip/tools/testing/selftests/rseq/basic_percpu_ops_test
 /usr/bin/ld: /tmp/ccuHTWnZ.o: in function `rseq_cmpeqv_storev':
 /home/mingo/tip/tools/testing/selftests/rseq/./rseq-x86.h:84: undefined
 reference to `.L8'
 /usr/bin/ld: /home/mingo/tip/tools/testing/selftests/rseq/./rseq-x86.h:84:
 undefined reference to `.L49'
 /usr/bin/ld: /tmp/ccuHTWnZ.o: in function `rseq_cmpnev_storeoffp_load':
 /home/mingo/tip/tools/testing/selftests/rseq/./rseq-x86.h:141: undefined
 reference to `.L57'
 /usr/bin/ld: /tmp/ccuHTWnZ.o:(__rseq_failure+0x8): undefined reference to `.L8'
 /usr/bin/ld: /tmp/ccuHTWnZ.o:(__rseq_failure+0x14): undefined reference to
 `.L49'
 /usr/bin/ld: /tmp/ccuHTWnZ.o:(__rseq_failure+0x20): undefined reference to
 `.L55'
 collect2: error: ld returned 1 exit status
 make: *** [Makefile:22:
 /home/mingo/tip/tools/testing/selftests/rseq/basic_percpu_ops_test] Error 1

Is this a known problem, or do I miss something from my build environment
perhaps? Vanilla 64-bit Ubuntu 18.10 (Cosmic).

It works fine with gcc-7 (gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3))
but indeed I get the same failure with gcc-8 (gcc version 8.0.1 20180414
(experimental) [trunk revision 259383] (Ubuntu 8-20180414-1ubuntu2)).

Thanks for reporting! I will investigate.

It looks like gcc-8 optimize away the target of asm goto labels when
there are more than one of them on x86-64. I'll try to come up with
a simpler reproducer.

It appears to be related to gcc-8 mishandling combination of
asm goto and thread-local storage input operands on x86-64.
Here is a simple reproducer:

__thread int var;
 
static int fct(void)
{
       asm goto (      "jmp %l[testlabel]\n\t"
                       : : [var] "m" (var) : : testlabel);
       return 0;
testlabel:

FWIW, if I add an empty

   asm volatile ("");

here after the label, gcc-8 -O2 builds "something" which is
a bogus assembler (an endless loop) :

main:
.LFB24:
        .cfi_startproc
.L2:
        subq    $8, %rsp
        .cfi_def_cfa_offset 16
#APP
# 6 "test-asm-goto.c" 1
        jmp .L2

# 0 "" 2
#NO_APP
        movl    %fs:var@tpoff, %edx
        leaq    .LC0(%rip), %rsi
        movl    $1, %edi
        xorl    %eax, %eax
        call    __printf_chk@PLT
        xorl    %eax, %eax
        addq    $8, %rsp
        .cfi_def_cfa_offset 8
        ret
        .cfi_endproc

Thoughts ?

Thanks,

Mathieu

       return 1;
}

int main()
{
       return fct();
}

building with gcc-7 -O2 is fine. Building with gcc-8 -O0 is
fine too. Building with gcc-8 -O1 and -O2 fails with:

/tmp/ccuXTFfs.o: In function `main':
test-asm-goto.c:(.text.startup+0x1): undefined reference to `.L2'
collect2: error: ld returned 1 exit status

With gcc-7 -O2, the assembly of main has the .L2 label:

main:
.LFB1:
       .cfi_startproc
#APP
# 5 "test-asm-goto.c" 1
       jmp .L2

# 0 "" 2
#NO_APP
.L4:
.L3:
       xorl    %eax, %eax
       ret
.L2:
       movl    $1, %eax
       ret
       .cfi_endproc

However, with gcc-8 -O2, it's missing:

main:
.LFB1:
       .cfi_startproc
.L3:
#APP
# 5 "test-asm-goto.c" 1
       jmp .L2

# 0 "" 2
#NO_APP
       xorl    %eax, %eax
       ret
       .cfi_endproc

It looks like we have a compiler issue. :-/

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com