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Violators will be prosecuted for from ; Thu, 12 Dec 2019 14:21:26 -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> From: Pierre Morel Date: Thu, 12 Dec 2019 15:21:21 +0100 MIME-Version: 1.0 In-Reply-To: <20191212151002.1c7ca4eb.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 15:10, 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. 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 - asynchrone ENABLE - failure to ENABLE > >> >>> 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)) - We need the enable to work (your proposition) to further test the I/O OK, I rework this part with your comment in mind. Thanks Pierre -- Pierre Morel IBM Lab Boeblingen