From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [PATCH 16/22] virtio_pci: use separate notification offsets for each vq. Date: Sat, 30 Mar 2013 13:49:00 +1030 Message-ID: <878v554lsr.fsf@rustcorp.com.au> References: <1363854584-25795-1-git-send-email-rusty@rustcorp.com.au> <1363854584-25795-17-git-send-email-rusty@rustcorp.com.au> <20130321101300.GA30493@redhat.com> <87wqt0du2e.fsf@rustcorp.com.au> <20130324201910.GA31631@redhat.com> <8738vjer43.fsf@rustcorp.com.au> <20130326193911.GA19251@redhat.com> <87ip4d4sef.fsf@rustcorp.com.au> <20130327112535.GE24243@redhat.com> <5153CC2E.3090908@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5153CC2E.3090908@zytor.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "H. Peter Anvin" , "Michael S. Tsirkin" Cc: virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org "H. Peter Anvin" writes: > On 03/27/2013 04:25 AM, Michael S. Tsirkin wrote: >> >> Aha. Yes, good idea. As for how large the offsets are, >> I am guessing we should either just say offset is vqn * X and data is >> vqn, or give hypervisors full flexibility with 32 bit offset and >> arbitrary data. >> 16 bit offsets seem neither here nor there ... > > Shift count? You can only have 2^16 vqs per device. Is it verboten to write 16-bit values to odd offsets? If so, we've just dropped it to 2^15 before you have to do some decoding to do. Hard to care... I dislike saying "multiply offset by 2" because implementations will get it wrong. That's because 0 will work either way, and that's going to be the common case. Cheers, Rusty.