From: "Michael S. Tsirkin" <mst@redhat.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: kvm@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
Sasha Levin <levinsasha928@gmail.com>,
virtualization@lists.linux-foundation.org, avi@redhat.com,
Anthony Liguori <anthony@codemonkey.ws>,
Thomas Lendacky <tahm@linux.vnet.ibm.com>
Subject: Re: [PATCH 0/3] virtio-net: inline header support
Date: Mon, 8 Oct 2012 23:31:15 +0200 [thread overview]
Message-ID: <20121008213114.GB17820@redhat.com> (raw)
In-Reply-To: <87391u3o67.fsf@rustcorp.com.au>
On Thu, Oct 04, 2012 at 01:04:56PM +0930, Rusty Russell wrote:
> Anthony Liguori <anthony@codemonkey.ws> writes:
> > Rusty Russell <rusty@rustcorp.com.au> writes:
> >
> >> "Michael S. Tsirkin" <mst@redhat.com> writes:
> >>
> >>> Thinking about Sasha's patches, we can reduce ring usage
> >>> for virtio net small packets dramatically if we put
> >>> virtio net header inline with the data.
> >>> This can be done for free in case guest net stack allocated
> >>> extra head room for the packet, and I don't see
> >>> why would this have any downsides.
> >>
> >> I've been wanting to do this for the longest time... but...
> >>
> >>> Even though with my recent patches qemu
> >>> no longer requires header to be the first s/g element,
> >>> we need a new feature bit to detect this.
> >>> A trivial qemu patch will be sent separately.
> >>
> >> There's a reason I haven't done this. I really, really dislike "my
> >> implemention isn't broken" feature bits. We could have an infinite
> >> number of them, for each bug in each device.
> >
> > This is a bug in the specification.
> >
> > The QEMU implementation pre-dates the specification. All of the actual
> > implementations of virtio relied on the semantics of s/g elements and
> > still do.
>
> lguest fix is pending in my queue. lkvm and qemu are broken; lkvm isn't
> ever going to be merged, so I'm not sure what its status is? But I'm
> determined to fix qemu, and hence my torture patch to make sure this
> doesn't creep in again.
If you look at my patch you'll notice there's also a
comment in virtio_net.h that seems to be broken in this respect:
/* This is the first element of the scatter-gather list. If you don't
* specify GSO or CSUM features, you can simply ignore the header. */
There is a similar comment in virtio-blk.
next prev parent reply other threads:[~2012-10-08 21:31 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-28 9:26 [PATCH 0/3] virtio-net: inline header support Michael S. Tsirkin
2012-09-28 9:26 ` [PATCH 1/3] virtio: add API to query ring capacity Michael S. Tsirkin
2012-09-28 9:26 ` [PATCH 2/3] virtio-net: correct capacity math on ring full Michael S. Tsirkin
2012-10-04 0:24 ` Rusty Russell
2012-09-28 9:26 ` [PATCH 3/3] virtio-net: put virtio net header inline with data Michael S. Tsirkin
2012-10-03 6:44 ` [PATCH 0/3] virtio-net: inline header support Rusty Russell
2012-10-03 7:10 ` Rusty Russell
2012-10-04 1:24 ` Anthony Liguori
2012-10-04 3:34 ` Rusty Russell
2012-10-04 4:29 ` Anthony Liguori
2012-10-04 7:44 ` Rusty Russell
2012-10-05 7:47 ` Paolo Bonzini
2012-10-08 21:31 ` Michael S. Tsirkin [this message]
2012-10-04 1:35 ` Anthony Liguori
2012-10-04 5:17 ` Rusty Russell
2012-10-08 20:41 ` Michael S. Tsirkin
[not found] ` <87vces2gxq.fsf__45058.6618776017$1349247807$gmane$org@rustcorp.com.au>
2012-10-03 10:53 ` Paolo Bonzini
2012-10-04 0:11 ` Rusty Russell
2012-10-04 7:09 ` Paolo Bonzini
2012-10-04 12:51 ` Rusty Russell
2012-10-04 13:23 ` Paolo Bonzini
2012-10-05 5:43 ` Rusty Russell
[not found] ` <87391t1nkq.fsf__40391.6521034718$1349505001$gmane$org@rustcorp.com.au>
2012-10-06 12:54 ` Paolo Bonzini
2012-10-09 4:59 ` Rusty Russell
2012-10-09 7:27 ` Paolo Bonzini
2012-10-11 0:03 ` Rusty Russell
2012-10-11 11:04 ` Michael S. Tsirkin
2012-10-11 22:37 ` Rusty Russell
2012-10-12 7:38 ` Paolo Bonzini
2012-10-12 11:52 ` Cornelia Huck
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