Re: [PATCH v2 08/10] s390x: smp: Wait for sigp completion

Janosch Frank
2020-04-29T08:57:54Z

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On 4/24/20 1:40 PM, Janosch Frank wrote:
> On 4/24/20 12:11 PM, David Hildenbrand wrote:
>> On 23.04.20 11:10, Janosch Frank wrote:
>>> Sigp orders are not necessarily finished when the processor finished
>>> the sigp instruction. We need to poll if the order has been finished
>>> before we continue.
>>>
>>> For (re)start and stop we already use sigp sense running and sigp
>>> sense loops. But we still lack completion checks for stop and store
>>> status, as well as the cpu resets.
>>>
>>> Let's add them.
>>>
>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>> ---
>>> lib/s390x/smp.c | 8 ++++++++
>>> lib/s390x/smp.h | 1 +
>>> s390x/smp.c | 4 ++++
>>> 3 files changed, 13 insertions(+)
>>>
>>> diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
>>> index 6ef0335..2555bf4 100644
>>> --- a/lib/s390x/smp.c
>>> +++ b/lib/s390x/smp.c
>>> @@ -154,6 +154,14 @@ int smp_cpu_start(uint16_t addr, struct psw psw)
>>> return rc;
>>> }
>>>
>>> +void smp_cpu_wait_for_completion(uint16_t addr)
>>> +{
>>> + uint32_t status;
>>> +
>>> + /* Loops when cc == 2, i.e. when the cpu is busy with a sigp order */
>>> + sigp_retry(1, SIGP_SENSE, 0, &status);
>>> +}
>>> +
>>> int smp_cpu_destroy(uint16_t addr)
>>> {
>>> struct cpu *cpu;
>>> diff --git a/lib/s390x/smp.h b/lib/s390x/smp.h
>>> index ce63a89..a8b98c0 100644
>>> --- a/lib/s390x/smp.h
>>> +++ b/lib/s390x/smp.h
>>> @@ -45,6 +45,7 @@ int smp_cpu_restart(uint16_t addr);
>>> int smp_cpu_start(uint16_t addr, struct psw psw);
>>> int smp_cpu_stop(uint16_t addr);
>>> int smp_cpu_stop_store_status(uint16_t addr);
>>> +void smp_cpu_wait_for_completion(uint16_t addr);
>>> int smp_cpu_destroy(uint16_t addr);
>>> int smp_cpu_setup(uint16_t addr, struct psw psw);
>>> void smp_teardown(void);
>>> diff --git a/s390x/smp.c b/s390x/smp.c
>>> index 7462211..48321f4 100644
>>> --- a/s390x/smp.c
>>> +++ b/s390x/smp.c
>>> @@ -75,6 +75,7 @@ static void test_stop_store_status(void)
>>> lc->prefix_sa = 0;
>>> lc->grs_sa[15] = 0;
>>> smp_cpu_stop_store_status(1);
>>> + smp_cpu_wait_for_completion(1);
>>> mb();
>>> report(lc->prefix_sa == (uint32_t)(uintptr_t)cpu->lowcore, "prefix");
>>> report(lc->grs_sa[15], "stack");
>>> @@ -85,6 +86,7 @@ static void test_stop_store_status(void)
>>> lc->prefix_sa = 0;
>>> lc->grs_sa[15] = 0;
>>> smp_cpu_stop_store_status(1);
>>
>> Just curious: Would it make sense to add that inside
>> smp_cpu_stop_store_status() instead?
>>
>
> I think so, we also wait for stop and start to finish, so why not for
> this order code.
>

I've moved the waiting into the smp library and now the prefix check for
stop and store status fails every so often if executed repeatedly.

I've tried making the lc ptr volatile, a print of the prefix before the
report seems to fix the issue, a print after the report still shows the
issue but according to the print both values are the same.

I'm currently at a loss...

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