Re: [kvm-unit-tests PATCH v3 7/9] s390x: css: msch, enable test

From: Pierre Morel <pmorel@linux.ibm.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org,
	frankja@linux.ibm.com, david@redhat.com, thuth@redhat.com
Subject: Re: [kvm-unit-tests PATCH v3 7/9] s390x: css: msch, enable test
Date: Tue, 10 Dec 2019 18:35:40 +0100	[thread overview]
Message-ID: <bf954926-fd77-9255-497b-44b825016a6f@linux.ibm.com> (raw)
In-Reply-To: <20191210100950.466e6211.cohuck@redhat.com>

On 2019-12-10 10:09, Cornelia Huck wrote:
> On Tue, 10 Dec 2019 10:01:46 +0100
> Pierre Morel <pmorel@linux.ibm.com> wrote:
> 
>> On 2019-12-09 17:54, Cornelia Huck wrote:
>>> On Fri,  6 Dec 2019 17:26:26 +0100
>>> Pierre Morel <pmorel@linux.ibm.com> wrote:
>>>    
>>>> A second step when testing the channel subsystem is to prepare a channel
>>>> for use.
>>>> This includes:
>>>> - Get the current SubCHannel Information Block (SCHIB) using STSCH
>>>> - Update it in memory to set the ENABLE bit
>>>> - Tell the CSS that the SCHIB has been modified using MSCH
>>>> - Get the SCHIB from the CSS again to verify that the subchannel is
>>>>     enabled.
>>>>
>>>> This tests the success of the MSCH instruction by enabling a channel.
>>>>
>>>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>>>> ---
>>>>    s390x/css.c | 39 +++++++++++++++++++++++++++++++++++++++
>>>>    1 file changed, 39 insertions(+)
>>>>
>>>> diff --git a/s390x/css.c b/s390x/css.c
>>>> index 3d4a986..4c0031c 100644
>>>> --- a/s390x/css.c
>>>> +++ b/s390x/css.c
>>>> @@ -58,11 +58,50 @@ static void test_enumerate(void)
>>>>    	report("Tested %d devices, %d found", 1, scn, found);
>>>>    }
>>>>    
>>>> +static void test_enable(void)
>>>> +{
>>>> +	struct pmcw *pmcw = &schib.pmcw;
>>>> +	int cc;
>>>> +
>>>> +	if (!test_device_sid) {
>>>> +		report_skip("No device");
>>>> +		return;
>>>> +	}
>>>> +	/* Read the SCIB for this subchannel */
>>>
>>> s/SCIB/SCHIB/
>>
>> yes
>>
>>>    
>>>> +	cc = stsch(test_device_sid, &schib);
>>>> +	if (cc) {
>>>> +		report("stsch cc=%d", 0, cc);
>>>> +		return;
>>>> +	}
>>>> +	/* Update the SCHIB to enable the channel */
>>>> +	pmcw->flags |= PMCW_ENABLE;
>>>> +
>>>> +	/* Tell the CSS we want to modify the subchannel */
>>>> +	cc = msch(test_device_sid, &schib);
>>>> +	if (cc) {
>>>> +		report("msch cc=%d", 0, cc);
>>>
>>> So you expect the subchannel to be idle? Probably true, especially as
>>> QEMU has no reason to post an unsolicited interrupt for a test device.
>>>    
>>>> +		return;
>>>> +	}
>>>> +
>>>> +	/* Read the SCHIB again to verify the enablement */
>>>> +	cc = stsch(test_device_sid, &schib);
>>>> +	if (cc) {
>>>> +		report("stsch cc=%d", 0, cc);
>>>> +		return;
>>>> +	}
>>>> +	if (!(pmcw->flags & PMCW_ENABLE)) {
>>>> +		report("Enable failed. pmcw: %x", 0, pmcw->flags);
>>>
>>> This check is fine when running under KVM. If this test is modified to
>>> run under z/VM in the future, you probably should retry here: I've seen
>>> the enable bit 'stick' only after the second msch() there.
>>
>> Oh. Thanks, may be I can loop with a delay and count.
> 
> FWIW, the Linux kernel code is trying 5 times.
> 
>> If I need to do this may be I need to create dedicated sub-functions to
>> include the sanity tests.
> 
> I'm not sure how worthwhile investing time here is, actually: If you
> don't plan to run under anything but KVM, you won't need it. I'm not
> sure if current versions of z/VM still display the same behaviour (it
> has been some time...); on the other hand, it is compliant with the
> architecture...

OK, I just insert the retry.

Thanks,
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen