Re: [kvm-unit-tests PATCH v3 7/9] s390x: smp: Remove unneeded cpu loops

Janosch Frank
2020-01-21T13:08:05Z

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On 1/21/20 1:59 PM, Cornelia Huck wrote:
> On Tue, 21 Jan 2020 13:46:51 +0100
> Janosch Frank <frankja@linux.ibm.com> wrote:
>
>> On 1/20/20 5:11 PM, Cornelia Huck wrote:
>>> On Mon, 20 Jan 2020 15:41:52 +0100
>>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>>
>>>> On 1/20/20 12:29 PM, Cornelia Huck wrote:
>>>>> On Fri, 17 Jan 2020 05:46:38 -0500
>>>>> Janosch Frank <frankja@linux.ibm.com> wrote:
>>>>>
>>>>>> Now that we have a loop which is executed after we return from the
>>>>>> main function of a secondary cpu, we can remove the surplus loops.
>>>>>>
>>>>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>>>>> ---
>>>>>> s390x/smp.c | 8 +-------
>>>>>> 1 file changed, 1 insertion(+), 7 deletions(-)
>>>>>>
>>>>>> diff --git a/s390x/smp.c b/s390x/smp.c
>>>>>> index 555ed72..c12a3db 100644
>>>>>> --- a/s390x/smp.c
>>>>>> +++ b/s390x/smp.c
>>>>>> @@ -29,15 +29,9 @@ static void wait_for_flag(void)
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> -static void cpu_loop(void)
>>>>>> -{
>>>>>> - for (;;) {}
>>>>>> -}
>>>>>> -
>>>>>> static void test_func(void)
>>>>>> {
>>>>>> testflag = 1;
>>>>>> - cpu_loop();
>>>>>> }
>>>>>>
>>>>>> static void test_start(void)
>>>>>> @@ -234,7 +228,7 @@ int main(void)
>>>>>>
>>>>>> /* Setting up the cpu to give it a stack and lowcore */
>>>>>> psw.mask = extract_psw_mask();
>>>>>> - psw.addr = (unsigned long)cpu_loop;
>>>>>> + psw.addr = (unsigned long)test_func;
>>>>>
>>>>> Before, you did not set testflag here... intended change?
>>>>
>>>> Yes
>>>> It is set to 0 before the first test, so it shouldn't matter.
>>>
>>> Hm... I got a bit lost in all those changes, so I checked your branch
>>> on github, and I don't see it being set to 0 before test_start() is
>>> called?
>>
>> Well, that's because test_start doesn't care about the flag.
>
> But I see a wait_for_flag() in there? What am I missing?
>
>> ecall and emcall are the first users, and they set it to 0 before using it.

Well, cpu #1 will update tesflag to 1 in ecall() and emcall()

>>
>>>
>>>>
>>>>>
>>>>>> smp_cpu_setup(1, psw);
>>>>>> smp_cpu_stop(1);
>>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>>
>

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