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

[Mathieu Desnoyers]

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

> ----- On Apr 19, 2019, at 8:55 AM, Mathieu Desnoyers
> mathieu.desnoyers@xxxxxxxxxxxx wrote:
> 
>> ----- On Apr 19, 2019, at 8:41 AM, Mathieu Desnoyers
>> mathieu.desnoyers@xxxxxxxxxxxx wrote:
>> 
>>> ----- On Apr 19, 2019, at 6:38 AM, Ingo Molnar mingo@xxxxxxxxxx wrote:
>>> 
>>>> * Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>>>> 
>>>>> 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@xxxxxxxxxxxx>
>>>>> Cc: Shuah Khan <shuah@xxxxxxxxxx>
>>>>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>>>>> Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
>>>>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>>>>> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>>>>> Cc: Dave Watson <davejwatson@xxxxxx>
>>>>> Cc: Will Deacon <will.deacon@xxxxxxx>
>>>>> Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
>>>>> Cc: linux-kselftest@xxxxxxxxxxxxxxx
>>>>> Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
>>>>> Cc: Chris Lameter <cl@xxxxxxxxx>
>>>>> Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
>>>>> Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
>>>>> Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
>>>>> Cc: Paul Turner <pjt@xxxxxxxxxx>
>>>>> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
>>>>> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>>>>> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
>>>>> Cc: Ben Maurer <bmaurer@xxxxxx>
>>>>> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>>>>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>>>>> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>>>>> ---
>>>>>  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