From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: Network performance with small packets Date: Thu, 14 Apr 2011 15:40:51 +0300 Message-ID: <20110414124051.GA9059@redhat.com> References: <20110127.130240.104065182.davem@davemloft.net> <20110202044222.GC3818@redhat.com> <201102091107.20270.rusty@rustcorp.com.au> <1299621444.25664.77.camel@localhost.localdomain> <1299637278.13202.61.camel@localhost.localdomain> <87fwqv4udl.fsf@rustcorp.com.au> <20110412200112.GA19729@redhat.com> <87bp09ax7a.fsf@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: habanero@linux.vnet.ibm.com, Shirley Ma , Krishna Kumar2 , David Miller , kvm@vger.kernel.org, netdev@vger.kernel.org, steved@us.ibm.com, Tom Lendacky , borntraeger@de.ibm.com To: Rusty Russell Return-path: Content-Disposition: inline In-Reply-To: <87bp09ax7a.fsf@rustcorp.com.au> Sender: kvm-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, Apr 14, 2011 at 08:58:41PM +0930, Rusty Russell wrote: > On Tue, 12 Apr 2011 23:01:12 +0300, "Michael S. Tsirkin" wrote: > > On Thu, Mar 10, 2011 at 12:19:42PM +1030, Rusty Russell wrote: > > > Here's an old patch where I played with implementing this: > > > > ... > > > > > > > > virtio: put last_used and last_avail index into ring itself. > > > > > > Generally, the other end of the virtio ring doesn't need to see where > > > you're up to in consuming the ring. However, to completely understand > > > what's going on from the outside, this information must be exposed. > > > For example, if you want to save and restore a virtio_ring, but you're > > > not the consumer because the kernel is using it directly. > > > > > > Fortunately, we have room to expand: > > > > This seems to be true for x86 kvm and lguest but is it true > > for s390? > > Yes, as the ring is page aligned so there's always room. > > > Will this last bit work on s390? > > If I understand correctly the memory is allocated by host there? > > They have to offer the feature, so if the have some way of allocating > non-page-aligned amounts of memory, they'll have to add those extra 2 > bytes. > > So I think it's OK... > Rusty. Correct. I wonder whether we need to pass the relevant flag to vring_size. If we do we'll need to add a new function for that though as vring_size is exported to userspace. -- MST