From: Anthony Liguori <anthony@codemonkey.ws>
To: Avi Kivity <avi@redhat.com>
Cc: Cam Macdonell <cam@cs.ualberta.ca>,
Paul Brook <paul@codesourcery.com>,
kvm@vger.kernel.org, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] Inter-VM shared memory PCI device
Date: Wed, 10 Mar 2010 11:13:45 -0600 [thread overview]
Message-ID: <4B97D349.1030105@codemonkey.ws> (raw)
In-Reply-To: <4B97659E.2090603@redhat.com>
On 03/10/2010 03:25 AM, Avi Kivity wrote:
> On 03/09/2010 11:44 PM, Anthony Liguori wrote:
>>> Ah yes. For cross tcg environments you can map the memory using
>>> mmio callbacks instead of directly, and issue the appropriate
>>> barriers there.
>>
>>
>> Not good enough unless you want to severely restrict the use of
>> shared memory within the guest.
>>
>> For instance, it's going to be useful to assume that you atomic
>> instructions remain atomic. Crossing architecture boundaries here
>> makes these assumptions invalid. A barrier is not enough.
>
> You could make the mmio callbacks flow to the shared memory server
> over the unix-domain socket, which would then serialize them. Still
> need to keep RMWs as single operations. When the host supports it,
> implement the operation locally (you can't render cmpxchg16b on i386,
> for example).
But now you have a requirement that the shmem server runs in lock-step
with the guest VCPU which has to happen for every single word of data
transferred.
You're much better off using a bulk-data transfer API that relaxes
coherency requirements. IOW, shared memory doesn't make sense for TCG :-)
Regards,
Anthony Liguori
next prev parent reply other threads:[~2010-03-10 17:14 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-05 23:52 [Qemu-devel] [PATCH] Support adding a file to qemu's ram allocation Cam Macdonell
2010-03-05 23:52 ` [Qemu-devel] [PATCH] Inter-VM shared memory PCI device Cam Macdonell
2010-03-07 22:53 ` Paul Brook
2010-03-08 1:45 ` Jamie Lokier
2010-03-08 9:48 ` Alexander Graf
2010-03-08 9:54 ` Jamie Lokier
2010-03-08 10:57 ` Alexander Graf
2010-03-09 21:41 ` Anthony Liguori
2010-03-08 13:04 ` Paul Brook
2010-03-09 19:00 ` Jamie Lokier
2010-03-08 9:52 ` Avi Kivity
2010-03-08 13:03 ` Paul Brook
2010-03-08 13:16 ` Avi Kivity
2010-03-09 20:11 ` Jamie Lokier
2010-03-09 21:44 ` Anthony Liguori
2010-03-10 9:25 ` Avi Kivity
2010-03-10 17:13 ` Anthony Liguori [this message]
2010-03-10 17:30 ` Avi Kivity
2010-03-10 17:41 ` Paul Brook
2010-03-11 6:33 ` Avi Kivity
2010-03-11 12:21 ` Paul Brook
2010-03-09 20:12 ` Jamie Lokier
2010-03-10 0:03 ` Paul Brook
2010-03-10 4:38 ` Cam Macdonell
2010-03-10 9:29 ` Avi Kivity
2010-03-10 11:13 ` Paul Brook
2010-03-11 3:10 ` Jamie Lokier
2010-03-11 4:37 ` Nick Piggin
2010-03-11 14:38 ` malc
2010-03-08 9:56 ` [Qemu-devel] " Avi Kivity
2010-03-08 17:57 ` Cam Macdonell
2010-03-09 10:29 ` Avi Kivity
[not found] ` <8286e4ee1003090724m1ef0b571g8b705a24e36e1753@mail.gmail.com>
2010-03-09 15:27 ` [Qemu-devel] " Cam Macdonell
2010-03-09 17:28 ` [Qemu-devel] " Avi Kivity
2010-03-09 17:34 ` Anthony Liguori
2010-03-09 18:34 ` Cam Macdonell
2010-03-10 9:21 ` Avi Kivity
2010-03-10 16:36 ` Cam Macdonell
2010-03-11 6:49 ` Avi Kivity
2010-03-09 12:49 ` Arnd Bergmann
2010-03-09 13:03 ` Avi Kivity
2010-03-09 16:44 ` Cam Macdonell
2010-03-10 14:04 ` Arnd Bergmann
2010-03-11 6:50 ` Avi Kivity
2010-03-11 12:57 ` Arnd Bergmann
2010-03-11 13:07 ` Avi Kivity
2010-03-11 14:32 ` Arnd Bergmann
2010-03-08 9:53 ` [Qemu-devel] Re: [PATCH] Support adding a file to qemu's ram allocation Avi Kivity
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