Re: [kvm-unit-tests PATCH v3 6/6] s390x: SMP test

David Hildenbrand
2019-09-25T13:35:21Z

On 25.09.19 15:32, David Hildenbrand wrote:
> On 25.09.19 15:30, Thomas Huth wrote:
>> On 25/09/2019 15.27, David Hildenbrand wrote:
>>> On 20.09.19 10:03, Janosch Frank wrote:
>>>> Testing SIGP emulation for the following order codes:
>>>> * start
>>>> * stop
>>>> * restart
>>>> * set prefix
>>>> * store status
>>>> * stop and store status
>>>> * reset
>>>> * initial reset
>>>> * external call
>>>> * emegergency call
>>>>
>>>> restart and set prefix are part of the library and needed to start
>>>> other cpus.
>>>>
>>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>>> ---
>>>> s390x/Makefile | 1 +
>>>> s390x/smp.c | 242 ++++++++++++++++++++++++++++++++++++++++++++
>>>> s390x/unittests.cfg | 4 +
>>>> 3 files changed, 247 insertions(+)
>>>> create mode 100644 s390x/smp.c
>>>>
>>>> diff --git a/s390x/Makefile b/s390x/Makefile
>>>> index d83dd0b..3744372 100644
>>>> --- a/s390x/Makefile
>>>> +++ b/s390x/Makefile
>>>> @@ -15,6 +15,7 @@ tests += $(TEST_DIR)/cpumodel.elf
>>>> tests += $(TEST_DIR)/diag288.elf
>>>> tests += $(TEST_DIR)/stsi.elf
>>>> tests += $(TEST_DIR)/skrf.elf
>>>> +tests += $(TEST_DIR)/smp.elf
>>>> tests_binary = $(patsubst %.elf,%.bin,$(tests))
>>>>
>>>> all: directories test_cases test_cases_binary
>>>> diff --git a/s390x/smp.c b/s390x/smp.c
>>>> new file mode 100644
>>>> index 0000000..7032494
>>>> --- /dev/null
>>>> +++ b/s390x/smp.c
>>>> @@ -0,0 +1,242 @@
>>>> +/*
>>>> + * Tests sigp emulation
>>>> + *
>>>> + * Copyright 2019 IBM Corp.
>>>> + *
>>>> + * Authors:
>>>> + * Janosch Frank <frankja@linux.ibm.com>
>>>> + *
>>>> + * This code is free software; you can redistribute it and/or modify it
>>>> + * under the terms of the GNU General Public License version 2.
>>>> + */
>>>> +#include <libcflat.h>
>>>> +#include <asm/asm-offsets.h>
>>>> +#include <asm/interrupt.h>
>>>> +#include <asm/page.h>
>>>> +#include <asm/facility.h>
>>>> +#include <asm-generic/barrier.h>
>>>> +#include <asm/sigp.h>
>>>> +
>>>> +#include <smp.h>
>>>> +#include <alloc_page.h>
>>>> +
>>>> +static int testflag = 0;
>>>> +
>>>> +static void cpu_loop(void)
>>>> +{
>>>> + for (;;) {}
>>>
>>> Won't that be optimized out completely?
>>
>> Why? AFAIK this is the standard way to write and endless loop ... how
>> can a compiler optimize that away?
>
> Was messing it up with "just" an empty loop body, I think you're right.
>

However

https://stackoverflow.com/questions/2178115/are-compilers-allowed-to-eliminate-infinite-loops

"This is intended to allow compiler transformations such as removal of
empty loops even when termination cannot be proven."

I think this might get optimized out.

--

Thanks,

David / dhildenb