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Violators will be prosecuted for from ; Thu, 12 Dec 2019 16:05:14 -0000 Subject: Re: [kvm-unit-tests PATCH v4 7/9] s390x: css: msch, enable test References: <1576079170-7244-1-git-send-email-pmorel@linux.ibm.com> <1576079170-7244-8-git-send-email-pmorel@linux.ibm.com> <20191212130111.0f75fe7f.cohuck@redhat.com> <83d45c31-30c3-36e1-1d68-51b88448f4af@linux.ibm.com> <20191212151002.1c7ca4eb.cohuck@redhat.com> <20191212153303.6444697e.cohuck@redhat.com> From: Pierre Morel Date: Thu, 12 Dec 2019 17:05:09 +0100 MIME-Version: 1.0 In-Reply-To: <20191212153303.6444697e.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: linux-s390-owner@vger.kernel.org List-ID: To: Cornelia Huck Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, david@redhat.com, thuth@redhat.com On 2019-12-12 15:33, Cornelia Huck wrote: > On Thu, 12 Dec 2019 15:21:21 +0100 > Pierre Morel wrote: > >> On 2019-12-12 15:10, Cornelia Huck wrote: >>> On Thu, 12 Dec 2019 15:01:07 +0100 >>> Pierre Morel wrote: >>> >>>> On 2019-12-12 13:01, Cornelia Huck wrote: >>>>> On Wed, 11 Dec 2019 16:46:08 +0100 >>>>> Pierre Morel 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 >>>>>> --- >>>>>> s390x/css.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++ >>>>>> 1 file changed, 65 insertions(+) >>> >>>>>> + /* Read the SCHIB for this subchannel */ >>>>>> + cc = stsch(test_device_sid, &schib); >>>>>> + if (cc) { >>>>>> + report(0, "stsch cc=%d", 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) { >>>>>> + /* >>>>>> + * If the subchannel is status pending or >>>>>> + * if a function is in progress, >>>>>> + * we consider both cases as errors. >>>>>> + */ >>>>>> + report(0, "msch cc=%d", cc); >>>>>> + return; >>>>>> + } >>>>>> + >>>>>> + /* >>>>>> + * Read the SCHIB again to verify the enablement >>>>>> + * insert a little delay and try 5 times. >>>>>> + */ >>>>>> + do { >>>>>> + cc = stsch(test_device_sid, &schib); >>>>>> + if (cc) { >>>>>> + report(0, "stsch cc=%d", cc); >>>>>> + return; >>>>>> + } >>>>>> + delay(10); >>>>> >>>>> That's just a short delay to avoid a busy loop, right? msch should be >>>>> immediate, >>>> >>>> Thought you told to me that it may not be immediate in zVM did I >>>> misunderstand? >>> >>> Maybe I have been confusing... what I'm referring to is this >>> programming note for msch: >>> >>> "It is recommended that the program inspect the >>> contents of the subchannel by subsequently >>> issuing STORE SUBCHANNEL when MODIFY >>> SUBCHANNEL sets condition code 0. Use of >>> STORE SUBCHANNEL is a method for deter- >>> mining if the designated subchannel was >>> changed or not. Failure to inspect the subchan- >>> nel following the setting of condition code 0 by >>> MODIFY SUBCHANNEL may result in conditions >>> that the program does not expect to occur." >>> >>> That's exactly what we had to do under z/VM back then: do the msch, >>> check via stsch, redo the msch if needed, check again via stsch. It >>> usually worked with the second msch the latest. >> >> OK, I understand, then it is a bug in zVM that this test could enlighten. > > Probably more a quirk than a bug... the explanation there is not > explicit about that :) > >> >> I think we should keep it so, it allows to recognize 3 cases (after I >> change to test ENABLE in the loop as I said I will): >> - immediate ENABLE > > This is the good case. > >> - asynchrone ENABLE > > This one I would consider an architecture violation. > >> - failure to ENABLE > > This is the quirk above. > > But I'm not quite sure how you would be able to distinguish the last > two cases? This is where the delay can help. But yes, not sure that we can differentiate this without to know how long we should delay. > >>> >>>> >>>>> and you probably should not delay on success? >>>> >>>> yes, it is not optimized, I can test PMCW_ENABLE in the loop this way we >>>> can see if, in the zVM case we need to do retries or not. >>>> >>>> >>>>> >>>>>> + } while (!(pmcw->flags & PMCW_ENABLE) && count++ < 5); >>>>> >>>>> How is this supposed to work? Doesn't the stsch overwrite the control >>>>> block again, so you need to re-set the enable bit before you retry? >>>> >>>> I do not think so, there is no msch() in the loop. >>>> Do I miss something? >>> >>> Well, _I_ missed that the msch() was missing :) You need it (see above); >>> just waiting and re-doing the stsch is useless, as msch is a >>> synchronous instruction which has finished its processing after the cc >>> has been set. >>> >> >> Since kvm-unit-test is a test system, not an OS so I think that here we >> have one more point to leverage the enable function: >> - We need to test the enable (what I did (partially)) > > Maybe also log if you needed to retry? Not as an error, but as > additional information? Yes. Regards, Pierre -- Pierre Morel IBM Lab Boeblingen