Date:   Fri, 19 Apr 2019 12:57:39 -0600
From:   shuah <shuah@...nel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        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>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        shuah <shuah@...nel.org>
Subject: Re: [PATCH for 5.1 3/3] rseq/selftests: Adapt number of threads to
 the number of detected cpus

On 4/19/19 8:40 AM, Mathieu Desnoyers wrote:
> ----- On Apr 19, 2019, at 10:17 AM, shuah shuah@...nel.org wrote:
> 
>> On 4/19/19 7:48 AM, Mathieu Desnoyers wrote:
>>> ----- 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 ?
>>>
>>
>> Didn't see problems when I tested it before applying it to
>> linux-kselftest next.
>>
>> I have gcc version 7.3.0 (Ubuntu 7.3.0-27ubuntu1~18.04)
> 
> It really appears to be an optimization bug in gcc-8. Considering that
> bogus compilers are released in the wild, we can hardly justify using
> the compiler feature that triggers the bogus behavior, even if it gets
> fixed in the future.
> 
> I've prepared a patch that changes the way the __rseq_abi fields are
> passed to the inline asm. I pass the address of the __rseq_abi TLS
> as a register input operand rather than each individual field as "m"
> operand.
> 
> I will submit it in a separate thread.
> 
> By the way, it affects both x86-32 (building with gcc-8 -m32) and x86-64.
> 

Should I drop this patch that is currently in linux-kseltest next? Just
confirming if your new patch is supposed to be applied on top of this
one or not?

thanks,
-- Shuah

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