From: Avi Kivity <avi@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: cam <cam@cs.ualberta.ca>,
David Evensky <evensky@dancer.ca.sandia.gov>,
Pekka Enberg <penberg@kernel.org>,
qemu-devel <qemu-devel@nongnu.org>, kvm <kvm@vger.kernel.org>
Subject: Re: [Qemu-devel] Questions regarding ivshmem spec
Date: Thu, 25 Aug 2011 17:40:31 +0300 [thread overview]
Message-ID: <4E565EDF.4080800@redhat.com> (raw)
In-Reply-To: <1314283146.3692.59.camel@lappy>
On 08/25/2011 05:39 PM, Sasha Levin wrote:
> On Thu, 2011-08-25 at 17:00 +0300, Avi Kivity wrote:
> > On 08/25/2011 04:29 PM, Sasha Levin wrote:
> > > 2. The spec describes DOORBELL as an array of DWORDs, when one guest
> > > wants to poke a different guest it would write something into the offset
> > > of the other guest in the DOORBELL array.
> > > Looking at the implementation in QEMU, DOORBELL is one DWORD, when
> > > writing to it the upper WORD is the guest id and the lower WORD is the
> > > value.
> > > What am I missing here?
> > >
> >
> > The spec in qemu.git is accurate. The intent is to use an ioeventfd
> > bound into an irqfd so a write into the doorbell injects an interrupt
> > directly into the other guest, without going through qemu^Wkvm tool.
> >
>
> But the doorbell is a single DWORD, so if a guest writes to it we'd
> still need to figure out which guest/vector he wants to poke from
> userspace, no?
>
> If it was an array of doorbells then yes, we could assign an ioeventfd
> to each offset - but now I don't quite see how we can avoid passing
> through the userspace.
>
Use the datamatch facility.
We didn't want an array of registers to avoid scaling issues (PIO space
is quite small).
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
WARNING: multiple messages have this Message-ID (diff)
From: Avi Kivity <avi@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
Cc: Pekka Enberg <penberg@kernel.org>, cam <cam@cs.ualberta.ca>,
qemu-devel <qemu-devel@nongnu.org>,
David Evensky <evensky@dancer.ca.sandia.gov>,
kvm <kvm@vger.kernel.org>
Subject: Re: [Qemu-devel] Questions regarding ivshmem spec
Date: Thu, 25 Aug 2011 17:40:31 +0300 [thread overview]
Message-ID: <4E565EDF.4080800@redhat.com> (raw)
In-Reply-To: <1314283146.3692.59.camel@lappy>
On 08/25/2011 05:39 PM, Sasha Levin wrote:
> On Thu, 2011-08-25 at 17:00 +0300, Avi Kivity wrote:
> > On 08/25/2011 04:29 PM, Sasha Levin wrote:
> > > 2. The spec describes DOORBELL as an array of DWORDs, when one guest
> > > wants to poke a different guest it would write something into the offset
> > > of the other guest in the DOORBELL array.
> > > Looking at the implementation in QEMU, DOORBELL is one DWORD, when
> > > writing to it the upper WORD is the guest id and the lower WORD is the
> > > value.
> > > What am I missing here?
> > >
> >
> > The spec in qemu.git is accurate. The intent is to use an ioeventfd
> > bound into an irqfd so a write into the doorbell injects an interrupt
> > directly into the other guest, without going through qemu^Wkvm tool.
> >
>
> But the doorbell is a single DWORD, so if a guest writes to it we'd
> still need to figure out which guest/vector he wants to poke from
> userspace, no?
>
> If it was an array of doorbells then yes, we could assign an ioeventfd
> to each offset - but now I don't quite see how we can avoid passing
> through the userspace.
>
Use the datamatch facility.
We didn't want an array of registers to avoid scaling issues (PIO space
is quite small).
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2011-08-25 14:40 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-25 13:29 Questions regarding ivshmem spec Sasha Levin
2011-08-25 13:29 ` [Qemu-devel] " Sasha Levin
2011-08-25 14:00 ` Avi Kivity
2011-08-25 14:00 ` Avi Kivity
2011-08-25 14:39 ` Sasha Levin
2011-08-25 14:39 ` Sasha Levin
2011-08-25 14:40 ` Avi Kivity [this message]
2011-08-25 14:40 ` Avi Kivity
2011-08-25 14:42 ` Sasha Levin
2011-08-25 14:42 ` [Qemu-devel] " Sasha Levin
2011-08-29 15:25 ` Sasha Levin
2011-08-29 15:25 ` [Qemu-devel] " Sasha Levin
2011-08-29 18:15 ` Cam Macdonell
2011-08-29 18:15 ` [Qemu-devel] " Cam Macdonell
2011-08-30 17:37 ` Cam Macdonell
2011-08-30 17:37 ` [Qemu-devel] " Cam Macdonell
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