From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:49406) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1goYVd-0006wd-8X for qemu-devel@nongnu.org; Tue, 29 Jan 2019 13:53:22 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1goYVc-0003RT-6d for qemu-devel@nongnu.org; Tue, 29 Jan 2019 13:53:21 -0500 Date: Tue, 29 Jan 2019 19:53:03 +0100 From: Cornelia Huck Message-ID: <20190129195303.72d5fbc4.cohuck@redhat.com> In-Reply-To: <691e91ea-df02-1455-93ed-7e8369fceec2@linux.ibm.com> References: <20190121110354.2247-1-cohuck@redhat.com> <20190121110354.2247-3-cohuck@redhat.com> <2dac6201-9e71-b188-0385-d09d05071a1c@linux.ibm.com> <5627cb78-22b3-0557-7972-256bc9560d86@linux.ibm.com> <20190125112437.2c06fac6.cohuck@redhat.com> <20190125135835.2d59b511.cohuck@redhat.com> <20190125150101.3b61f0a1@oc2783563651> <20190128180948.506a9695.cohuck@redhat.com> <20190128201548.1ecfb84f@oc2783563651> <20190129112024.401b8184.cohuck@redhat.com> <691e91ea-df02-1455-93ed-7e8369fceec2@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Farman Cc: Halil Pasic , Farhan Ali , Pierre Morel , linux-s390@vger.kernel.org, kvm@vger.kernel.org, qemu-devel@nongnu.org, qemu-s390x@nongnu.org, Alex Williamson On Tue, 29 Jan 2019 09:14:40 -0500 Eric Farman wrote: > On 01/29/2019 05:20 AM, Cornelia Huck wrote: > > On Mon, 28 Jan 2019 16:48:10 -0500 > > Eric Farman wrote: > > > >> On 01/28/2019 02:15 PM, Halil Pasic wrote: > >>> On Mon, 28 Jan 2019 18:09:48 +0100 > >>> Cornelia Huck wrote: > > > >> I guess if > >>> the ssch() returns with non cc == 0 the CP_PENDING ---IRQ---> IDLE > >>> transition > >>> won't take place. And I guess the IRQ is a final one. > >> > >> Yes this is the one point I hadn't seen explicitly stated. We shouldn't > >> remain in state=BUSY if the ssch got cc!=0, and probably return to IDLE > >> when processing the failure. In Connie's response (Mon, 28 Jan 2019 > >> 18:24:24 +0100) to my note, she expressed some agreement to that. > > > > Yes, I think that's what should happen. > > > > > >>>> state for I/O) > >>>> (normal ssch) > >>>> > >>>> BUSY --- IO_REQ ---> return -EAGAIN, stay in BUSY > >>>> (user space is supposed to retry, as we'll eventually progress from > >>>> BUSY) > >>>> > >>>> CP_PENDING --- IO_REQ ---> return -EBUSY, stay in CP_PENDING > >>>> (user space is supposed to map this to the appropriate cc for the guest) > >>> > >>> From this it seems you don't intend to issue the second requested ssch() > >>> any more (and don't want to do any translation). Is that right? (If it > >>> is, that what I was asking for for a while, but then it's a pity for the > >>> retries.) > >>> > >>>> > >>>> IDLE --- ASYNC_REQ ---> IDLE > >>>> (user space is welcome to do anything else right away) > >>> > >>> Your idea is to not issue a requested hsch() if we think we are IDLE > >>> it seems. Do I understand this right? We would end up with a different > >>> semantic for hsch()/and csch() (compared to PoP) in the guest with this > >>> (AFAICT). > >>> > >>>> > >>>> BUSY --- ASYNC_REQ ---> return -EAGAIN, stay in BUSY > >>>> (user space is supposed to retry, as above) > >>>> > >>>> CP_PENDING --- ASYNC_REQ ---> return success, stay in CP_PENDING > >>>> (the interrupt will get us out of CP_PENDING eventually) > >>> > >>> Issue (c|h)sch() is an action that is done on this internal > >>> transition (within CP_PENDING). > >> > >> These three do read like CSCH/HSCH are subject to the same rules as > >> SSCH, when in fact they would be (among other reasons) issued to clean > >> up a lost interrupt from a previous SSCH. So maybe return -EAGAIN on > >> state=BUSY (don't race ourselves with the start), but issue to hardware > >> if CP_PENDING. > > > > I think there are some devices which require a certain hsch/csch > > sequence during device bringup, so it's not just cleaning up after a > > ssch. > > Ah, yes. > > Therefore, we should always try to do the requested hsch/csch, > > unless things like "we're in the process of translating a cp, and can't > > deal with another request right now" prevent it. > > Agreed. I'm in support of all of this. Cool. In the meantime, I've coded the changes, and I think the result looks reasonable. I'll give it some testing and then send it out; it's probably easier to discuss it with some code in front of us. [The QEMU part should not need any changes.] > > > > >> > >> If we get an async request when state=IDLE, then maybe just issue it for > >> fun, as if it were an SSCH? > > > > For fun, but mainly because the guest wants it :) > > > > Well, that too. ;-) >