[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling

From: Eric Farman
Subject: Re: [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling
Date: Tue, 29 Jan 2019 09:14:40 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 01/29/2019 05:20 AM, Cornelia Huck wrote:
On Mon, 28 Jan 2019 16:48:10 -0500
Eric Farman <address@hidden> wrote:

On 01/28/2019 02:15 PM, Halil Pasic wrote:
On Mon, 28 Jan 2019 18:09:48 +0100
Cornelia Huck <address@hidden> wrote:

I guess if
the ssch() returns with non cc == 0 the CP_PENDING ---IRQ---> IDLE
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

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

(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

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

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

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.

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.  ;-)

reply via email to

[Prev in Thread] Current Thread [Next in Thread]