Re: [kvm-unit-tests PATCH v3 2/2] s390x: Test specification exceptions during transaction

[Janis Schoetterl-Glausch <scgl@linux.vnet.ibm.com>]

On 10/25/21 19:30, Claudio Imbrenda wrote:
> On Fri, 22 Oct 2021 14:01:56 +0200
> Janis Schoetterl-Glausch <scgl@linux.ibm.com> wrote:
> 
>> Program interruptions during transactional execution cause other
>> interruption codes.
>> Check that we see the expected code for (some) specification exceptions.
>>
>> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
>> ---

[...]

>> +#define TRANSACTION_MAX_RETRIES 5
>> +
>> +/* NULL must be passed to __builtin_tbegin via constant, forbid diagnose from
>> + * being NULL to keep things simple
>> + */
>> +static int __attribute__((nonnull))
>> +with_transaction(void (*trigger)(void), struct __htm_tdb *diagnose)
>> +{
>> +	int cc;
>> +
> 
> if you want to be extra sure, put an assert here (although I'm not sure
> how nonnull works, I have never seen it before)

Ok, with nonnull, the compiler might warn you if you pass NULL.
> 
>> +	cc = __builtin_tbegin(diagnose);
>> +	if (cc == _HTM_TBEGIN_STARTED) {
>> +		trigger();
>> +		__builtin_tend();
>> +		return -TRANSACTION_COMPLETED;
>> +	} else {
>> +		return -cc;
>> +	}
>> +}
>> +
>> +static int retry_transaction(const struct spec_ex_trigger *trigger, unsigned int max_retries,
>> +			     struct __htm_tdb *tdb, uint16_t expected_pgm)
>> +{
>> +	int trans_result, i;
>> +	uint16_t pgm;
>> +
>> +	for (i = 0; i < max_retries; i++) {
>> +		expect_pgm_int();
>> +		trans_result = with_transaction(trigger->func, tdb);
>> +		if (trans_result == -_HTM_TBEGIN_TRANSIENT) {
>> +			mb();
>> +			pgm = lc->pgm_int_code;
>> +			if (pgm == 0)
>> +				continue;
>> +			else if (pgm == expected_pgm)
>> +				return 0;
>> +		}
>> +		return trans_result;
>> +	}
>> +	return -TRANSACTION_MAX_RETRIES;
> 
> so this means that a test will be considered failed if the transaction
> failed too many times?

Yes.
> 
> this means that could fail if the test is run on busy system, even if
> the host running the unit test is correct

I suppose so, don't know how likely that is.
> 
> also, do you really need to use negative values? it's probably easier
> to read if you stick to positive values, and less prone to mistakes if
> you accidentally forget a - somewhere.

Ok.
> 
>> +}
>> +
>> +static void test_spec_ex_trans(struct args *args, const struct spec_ex_trigger *trigger)
>> +{
>> +	const uint16_t expected_pgm = PGM_INT_CODE_SPECIFICATION
>> +			      | PGM_INT_CODE_TX_ABORTED_EVENT;
>> +	union {
>> +		struct __htm_tdb tdb;
>> +		uint64_t dwords[sizeof(struct __htm_tdb) / sizeof(uint64_t)];
>> +	} diag;
>> +	unsigned int i, failures = 0;
>> +	int trans_result;
>> +
>> +	if (!test_facility(73)) {
>> +		report_skip("transactional-execution facility not installed");
>> +		return;
>> +	}
>> +	ctl_set_bit(0, CTL0_TRANSACT_EX_CTL); /* enable transactional-exec */
>> +
>> +	for (i = 0; i < args->iterations && failures <= args->max_failures; i++) {
>> +		register_pgm_cleanup_func(trigger->fixup);
>> +		trans_result = retry_transaction(trigger, args->max_retries, &diag.tdb, expected_pgm);
> 
> so you retry each iteration up to args->max_retries times, and if a
> transaction aborts too many times (maybe because the host system is
> very busy), then you consider it a fail
> 

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