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

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Date:   Fri, 19 Apr 2019 08:55:07 -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 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.

Thanks,

Mathieu


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