From: "Michael S. Tsirkin" <mst@redhat.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Asias He <asias@redhat.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 08/16] virtio_ring: virtqueue_add_outbuf / virtqueue_add_inbuf.
Date: Mon, 25 Feb 2013 23:35:04 +0200 [thread overview]
Message-ID: <20130225213504.GC18167@redhat.com> (raw)
In-Reply-To: <87sj4pfc61.fsf@rustcorp.com.au>
On Fri, Feb 22, 2013 at 10:32:46AM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> > On Tue, Feb 19, 2013 at 06:26:26PM +1030, Rusty Russell wrote:
> >> These are specialized versions of virtqueue_add_buf(), which cover
> >> over 50% of cases and are far clearer.
> >>
> >> In particular, the scatterlists passed to these functions don't have
> >> to be clean (ie. we ignore end markers).
> >>
> >> FIXME: I'm not sure about the unclean sglist bit. I had a more
> >> ambitious one which conditionally ignored end markers in the iterator,
> >> but it was ugly and I suspect this is just as fast. Maybe we should
> >> just fix all the drivers?
> >>
> >> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> >
> > Looking at code, it seems that most users really have a single sg, in
> > low memory. So how about simply passing void * instead of sg? Whoever
> > has multiple sgs can use the rich interface.
>
> Good point, let's do that:
> 1) Make virtqueue_add_outbuf()/inbuf() take a void * and len.
> 2) Transfer users across to use that.
> 3) Make everyone else use clean scatterlists with virtqueue_add_sgs[].
> 4) Remove virtqueue_add_bufs().
>
> > Long term we might optimize this unrolling some loops, I think
> > I saw this giving a small performance gain for -net.
>
> I *think* we could make virtqueue_add() an inline and implement an
> virtqueue_add_outsg() wrapper and gcc will eliminate the loops for us.
> But not sure it's worth the text bloat...
>
> Cheers,
> Rusty.
inline is mostly useless nowdays... We can make it a static function and
let gcc decide.
--
MST
next prev parent reply other threads:[~2013-02-25 21:34 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-19 7:56 [PATCH 00/16] virtio ring rework Rusty Russell
2013-02-19 7:56 ` [PATCH 01/16] scatterlist: introduce sg_unmark_end Rusty Russell
2013-02-19 7:56 ` [PATCH 02/16] virtio_ring: virtqueue_add_sgs, to add multiple sgs Rusty Russell
2013-02-19 9:15 ` Wanlong Gao
2013-02-20 9:18 ` Asias He
2013-02-24 22:12 ` Michael S. Tsirkin
2013-02-26 5:14 ` Rusty Russell
2013-02-26 9:30 ` Michael S. Tsirkin
2013-02-26 7:02 ` Paolo Bonzini
2013-02-27 7:28 ` Rusty Russell
2013-02-27 7:49 ` Michael S. Tsirkin
2013-02-27 11:21 ` Rusty Russell
2013-02-28 9:24 ` Paolo Bonzini
2013-03-01 1:01 ` Rusty Russell
2013-02-19 7:56 ` [PATCH 03/16] virtio-blk: reorganize virtblk_add_req Rusty Russell
2013-02-19 7:56 ` [PATCH 04/16] virtio-blk: use virtqueue_start_buf on bio path Rusty Russell
2013-02-20 9:19 ` Asias He
2013-02-21 6:23 ` Rusty Russell
2013-02-19 7:56 ` [PATCH 05/16] virtio-blk: use virtqueue_add_sgs on req path Rusty Russell
2013-02-20 9:20 ` Asias He
2013-02-19 7:56 ` [PATCH 06/16] virtio_blk: remove nents member Rusty Russell
2013-02-20 9:20 ` Asias He
2013-02-19 7:56 ` [PATCH 07/16] virtio_ring: don't count elements twice for add_buf path Rusty Russell
2013-02-20 10:09 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 08/16] virtio_ring: virtqueue_add_outbuf / virtqueue_add_inbuf Rusty Russell
2013-02-20 10:09 ` Wanlong Gao
2013-02-21 17:09 ` Michael S. Tsirkin
2013-02-22 0:02 ` Rusty Russell
2013-02-25 21:35 ` Michael S. Tsirkin [this message]
2013-02-28 5:08 ` Rusty Russell
2013-02-28 7:01 ` Michael S. Tsirkin
2013-03-06 6:03 ` Rusty Russell
2013-02-19 7:56 ` [PATCH 09/16] virtio_net: use simplified virtqueue accessors Rusty Russell
2013-02-20 10:09 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 10/16] virtio_net: use virtqueue_add_sgs[] for command buffers Rusty Russell
2013-02-20 10:11 ` Wanlong Gao
2013-02-21 6:27 ` Rusty Russell
2013-02-21 8:30 ` Wanlong Gao
2013-02-21 9:41 ` Jason Wang
2013-02-21 9:43 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 11/16] virtio_rng: use simplified virtqueue accessors Rusty Russell
2013-02-20 10:12 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 12/16] virtio_console: " Rusty Russell
2013-02-20 10:12 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 13/16] caif_virtio: " Rusty Russell
2013-02-20 10:13 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 14/16] virtio_rpmsg_bus: " Rusty Russell
2013-02-20 10:14 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 15/16] virtio_balloon: " Rusty Russell
2013-02-20 10:15 ` Wanlong Gao
2013-02-19 7:56 ` [PATCH 16/16] 9p/trans_virtio.c: use virtio_add_sgs[] Rusty Russell
2013-02-19 9:15 ` [PATCH 00/16] virtio ring rework Paolo Bonzini
2013-02-21 6:30 ` Rusty Russell
2013-02-20 8:37 ` [PATCH 17/16] virtio-scsi: use virtqueue_add_sgs for command buffers Wanlong Gao
2013-02-20 9:38 ` Asias He
2013-02-20 9:41 ` Wanlong Gao
2013-02-20 9:47 ` [PATCH 17/16 V2] " Wanlong Gao
2013-02-20 10:54 ` Paolo Bonzini
2013-02-20 12:17 ` Asias He
2013-02-21 6:34 ` Rusty Russell
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