From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:33147) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qwb8C-0003Sj-Sy for qemu-devel@nongnu.org; Thu, 25 Aug 2011 10:42:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Qwb8B-0005VB-IA for qemu-devel@nongnu.org; Thu, 25 Aug 2011 10:42:08 -0400 Received: from mail-fx0-f45.google.com ([209.85.161.45]:36447) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qwb8B-0005V2-DC for qemu-devel@nongnu.org; Thu, 25 Aug 2011 10:42:07 -0400 Received: by fxbb27 with SMTP id b27so2033432fxb.4 for ; Thu, 25 Aug 2011 07:42:06 -0700 (PDT) From: Sasha Levin In-Reply-To: <4E565EDF.4080800@redhat.com> References: <1314278954.3692.55.camel@lappy> <4E56556E.1080805@redhat.com> <1314283146.3692.59.camel@lappy> <4E565EDF.4080800@redhat.com> Content-Type: text/plain; charset="us-ascii" Date: Thu, 25 Aug 2011 17:42:03 +0300 Message-ID: <1314283323.3692.60.camel@lappy> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Questions regarding ivshmem spec List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Pekka Enberg , cam , qemu-devel , David Evensky , kvm On Thu, 2011-08-25 at 17:40 +0300, Avi Kivity wrote: > 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). > > Ah, right. Thanks! -- Sasha.