Re: [kvm-unit-tests PATCH v4 2/9] s390x: smp: Only use smp_cpu_setup once

David Hildenbrand
2020-01-24T08:28:09Z

On 23.01.20 14:56, David Hildenbrand wrote:
> On 23.01.20 14:54, Janosch Frank wrote:
>> On 1/23/20 2:45 PM, David Hildenbrand wrote:
>>> On 21.01.20 14:42, Janosch Frank wrote:
>>>> Let's stop and start instead of using setup to run a function on a
>>>> cpu.
>>>>
>>>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>>>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>>> Acked-by: David Hildenbrand <david@redhat.com>
>>>> ---
>>>> s390x/smp.c | 21 ++++++++++++++-------
>>>> 1 file changed, 14 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/s390x/smp.c b/s390x/smp.c
>>>> index e37eb56..3e8cf3e 100644
>>>> --- a/s390x/smp.c
>>>> +++ b/s390x/smp.c
>>>> @@ -53,7 +53,7 @@ static void test_start(void)
>>>> psw.addr = (unsigned long)test_func;
>>>>
>>>> set_flag(0);
>>>> - smp_cpu_setup(1, psw);
>>>> + smp_cpu_start(1, psw);
>>>> wait_for_flag();
>>>> report(1, "start");
>>>> }
>>>> @@ -109,6 +109,7 @@ static void test_store_status(void)
>>>> report(1, "status written");
>>>> free_pages(status, PAGE_SIZE * 2);
>>>> report_prefix_pop();
>>>> + smp_cpu_stop(1);
>>>>
>>>> report_prefix_pop();
>>>> }
>>>> @@ -137,9 +138,8 @@ static void test_ecall(void)
>>>>
>>>> report_prefix_push("ecall");
>>>> set_flag(0);
>>>> - smp_cpu_destroy(1);
>>>>
>>>> - smp_cpu_setup(1, psw);
>>>> + smp_cpu_start(1, psw);
>>>> wait_for_flag();
>>>> set_flag(0);
>>>> sigp(1, SIGP_EXTERNAL_CALL, 0, NULL);
>>>> @@ -172,9 +172,8 @@ static void test_emcall(void)
>>>>
>>>> report_prefix_push("emcall");
>>>> set_flag(0);
>>>> - smp_cpu_destroy(1);
>>>>
>>>> - smp_cpu_setup(1, psw);
>>>> + smp_cpu_start(1, psw);
>>>> wait_for_flag();
>>>> set_flag(0);
>>>> sigp(1, SIGP_EMERGENCY_SIGNAL, 0, NULL);
>>>> @@ -192,7 +191,7 @@ static void test_reset_initial(void)
>>>> psw.addr = (unsigned long)test_func;
>>>>
>>>> report_prefix_push("reset initial");
>>>> - smp_cpu_setup(1, psw);
>>>> + smp_cpu_start(1, psw);
>>>>
>>>> sigp_retry(1, SIGP_INITIAL_CPU_RESET, 0, NULL);
>>>> sigp(1, SIGP_STORE_STATUS_AT_ADDRESS, (uintptr_t)status, NULL);
>>>> @@ -223,7 +222,7 @@ static void test_reset(void)
>>>> psw.addr = (unsigned long)test_func;
>>>>
>>>> report_prefix_push("cpu reset");
>>>> - smp_cpu_setup(1, psw);
>>>> + smp_cpu_start(1, psw);
>>>>
>>>> sigp_retry(1, SIGP_CPU_RESET, 0, NULL);
>>>> report(smp_cpu_stopped(1), "cpu stopped");
>>>> @@ -232,6 +231,7 @@ static void test_reset(void)
>>>>
>>>> int main(void)
>>>> {
>>>> + struct psw psw;
>>>> report_prefix_push("smp");
>>>>
>>>> if (smp_query_num_cpus() == 1) {
>>>> @@ -239,6 +239,12 @@ int main(void)
>>>> goto done;
>>>> }
>>>>
>>>> + /* Setting up the cpu to give it a stack and lowcore */
>>>> + psw.mask = extract_psw_mask();
>>>> + psw.addr = (unsigned long)cpu_loop;
>>>> + smp_cpu_setup(1, psw);
>>>> + smp_cpu_stop(1);
>>>> +
>>>> test_start();
>>>> test_stop();
>>>> test_stop_store_status();
>>>> @@ -247,6 +253,7 @@ int main(void)
>>>> test_emcall();
>>>> test_reset();
>>>> test_reset_initial();
>>>> + smp_cpu_destroy(1);
>>>>
>>>> done:
>>>> report_prefix_pop();
>>>>
>>>
>>> With this patch, I get timeouts under TCG. Seems to loop forever.
>>>
>> The branch works on lpar and kvm without a problem.
>
> Which could mean that either TCG is broken or your test is broken (e.g.,
> a race condition that does not trigger under LPAR because it's faster,
> or some undocumented/not guaranteed behavior).
>

So, the test works every now and then under TCG.

It seems to work very reliably with "-smp 2"

With smp 8, it sometimes works, sometimes not.

t480s: ~/git/kvm-unit-tests (kein Branch, Rebase von s390x-prep) $
./s390x-run s390x/smp.elf -smp 8
/home/dhildenb/git/qemu/s390x-softmmu/qemu-system-s390x -nodefaults
-nographic -machine s390-ccw-virtio,accel=tcg -chardev stdio,id=con0
-device sclpconsole,chardev=con0 -kernel s390x/smp.elf -smp 8 # -initrd
/tmp/tmp.UL9ZaqoKBW
SMP: Initializing, found 8 cpus
PASS: smp: start
PASS: smp: stop
PASS: smp: stop store status: prefix
PASS: smp: stop store status: stack
PASS: smp: store status at address: running: incorrect state
PASS: smp: store status at address: running: status not written
PASS: smp: store status at address: stopped: status written
PASS: smp: ecall: ecall
PASS: smp: emcall: ecall
PASS: smp: cpu reset: cpu stopped
PASS: smp: reset initial: clear: psw
PASS: smp: reset initial: clear: prefix
PASS: smp: reset initial: clear: fpc
PASS: smp: reset initial: clear: cpu timer
PASS: smp: reset initial: clear: todpr
PASS: smp: reset initial: initialized: cr0 == 0xE0
PASS: smp: reset initial: initialized: cr14 == 0xC2000000
PASS: smp: reset initial: cpu stopped
SUMMARY: 18 tests

EXIT: STATUS=1

t480s: ~/git/kvm-unit-tests (kein Branch, Rebase von s390x-prep) $
./s390x-run s390x/smp.elf -smp 8
/home/dhildenb/git/qemu/s390x-softmmu/qemu-system-s390x -nodefaults
-nographic -machine s390-ccw-virtio,accel=tcg -chardev stdio,id=con0
-device sclpconsole,chardev=con0 -kernel s390x/smp.elf -smp 8 # -initrd
/tmp/tmp.csifrEDgnC
SMP: Initializing, found 8 cpus
PASS: smp: start
PASS: smp: stop
PASS: smp: stop store status: prefix
FAIL: smp: stop store status: stack
PASS: smp: store status at address: running: incorrect state
PASS: smp: store status at address: running: status not written
PASS: smp: store status at address: stopped: status written
[... hang]

Note that there is a previous failure for "smp: stop store status:
stack" whenever the test will hang later.

--
Thanks,

David / dhildenb