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Date: Fri, 19 Apr 2019 09:48:43 -0400 (EDT)
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-api <linux-api@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Boqun Feng <boqun.feng@...il.com>,
Andy Lutomirski <luto@...capital.net>,
Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Russell King <linux@....linux.org.uk>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
rostedt <rostedt@...dmis.org>,
Josh Triplett <josh@...htriplett.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Michael Kerrisk <mtk.manpages@...il.com>,
Joel Fernandes <joelaf@...gle.com>, shuah <shuah@...nel.org>,
linux-kselftest <linux-kselftest@...r.kernel.org>
Subject: 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@...icios.com wrote:
> ----- On Apr 19, 2019, at 8:55 AM, Mathieu Desnoyers
> mathieu.desnoyers@...icios.com wrote:
>
>> ----- On Apr 19, 2019, at 8:41 AM, Mathieu Desnoyers
>> mathieu.desnoyers@...icios.com wrote:
>>
>>> ----- On Apr 19, 2019, at 6:38 AM, Ingo Molnar mingo@...nel.org wrote:
>>>
>>>> * Mathieu Desnoyers <mathieu.desnoyers@...icios.com> 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@...icios.com>
>>>>> Cc: Shuah Khan <shuah@...nel.org>
>>>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>>>> Cc: Joel Fernandes <joelaf@...gle.com>
>>>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>>>> Cc: Catalin Marinas <catalin.marinas@....com>
>>>>> Cc: Dave Watson <davejwatson@...com>
>>>>> Cc: Will Deacon <will.deacon@....com>
>>>>> Cc: Andi Kleen <andi@...stfloor.org>
>>>>> Cc: linux-kselftest@...r.kernel.org
>>>>> Cc: "H . Peter Anvin" <hpa@...or.com>
>>>>> Cc: Chris Lameter <cl@...ux.com>
>>>>> Cc: Russell King <linux@....linux.org.uk>
>>>>> Cc: Michael Kerrisk <mtk.manpages@...il.com>
>>>>> Cc: "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
>>>>> Cc: Paul Turner <pjt@...gle.com>
>>>>> Cc: Boqun Feng <boqun.feng@...il.com>
>>>>> Cc: Josh Triplett <josh@...htriplett.org>
>>>>> Cc: Steven Rostedt <rostedt@...dmis.org>
>>>>> Cc: Ben Maurer <bmaurer@...com>
>>>>> Cc: Andy Lutomirski <luto@...capital.net>
>>>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>>>> Cc: Linus Torvalds <torvalds@...ux-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@...ff, %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
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