linux-kernel - Re: [RFC V3 PATCH 0/8] Packed ring for vhost

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Date:   Mon, 23 Apr 2018 16:11:51 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, tiwei.bie@...el.com,
        jfreimann@...hat.com, wexu@...hat.com
Subject: Re: [RFC V3 PATCH 0/8] Packed ring for vhost

On Mon, Apr 23, 2018 at 10:59:43PM +0300, Michael S. Tsirkin wrote:
> On Mon, Apr 23, 2018 at 03:31:20PM -0400, Konrad Rzeszutek Wilk wrote:
> > On Mon, Apr 23, 2018 at 01:34:52PM +0800, Jason Wang wrote:
> > > Hi all:
> > > 
> > > This RFC implement packed ring layout. The code were tested with
> > > Tiwei's RFC V2 a thttps://lkml.org/lkml/2018/4/1/48. Some fixups and
> > > tweaks were needed on top of Tiwei's code to make it run. TCP stream
> > > and pktgen does not show obvious difference compared with split ring.
> > 
> > I have to ask then - what is the benefit of this?
> 
> You can use this with dpdk within guest.
> The DPDK version did see a performance improvement so hopefully with

Is there a link to this performance improvement document?

> future versions this will too.
> 
> > > 
> > > Changes from V2:
> > > - do not use & in checking desc_event_flags
> > > - off should be most significant bit
> > > - remove the workaround of mergeable buffer for dpdk prototype
> > > - id should be in the last descriptor in the chain
> > > - keep _F_WRITE for write descriptor when adding used
> > > - device flags updating should use ADDR_USED type
> > > - return error on unexpected unavail descriptor in a chain
> > > - return false in vhost_ve_avail_empty is descriptor is available
> > > - track last seen avail_wrap_counter
> > > - correctly examine available descriptor in get_indirect_packed()
> > > - vhost_idx_diff should return u16 instead of bool
> > > 
> > > Changes from V1:
> > > 
> > > - Refactor vhost used elem code to avoid open coding on used elem
> > > - Event suppression support (compile test only).
> > > - Indirect descriptor support (compile test only).
> > > - Zerocopy support.
> > > - vIOMMU support.
> > > - SCSI/VSOCK support (compile test only).
> > > - Fix several bugs
> > > 
> > > For simplicity, I don't implement batching or other optimizations.
> > > 
> > > Please review.
> > > 
> > > Jason Wang (8):
> > >   vhost: move get_rx_bufs to vhost.c
> > >   vhost: hide used ring layout from device
> > >   vhost: do not use vring_used_elem
> > >   vhost_net: do not explicitly manipulate vhost_used_elem
> > >   vhost: vhost_put_user() can accept metadata type
> > >   virtio: introduce packed ring defines
> > >   vhost: packed ring support
> > >   vhost: event suppression for packed ring
> > > 
> > >  drivers/vhost/net.c                | 136 ++----
> > >  drivers/vhost/scsi.c               |  62 +--
> > >  drivers/vhost/vhost.c              | 824 ++++++++++++++++++++++++++++++++++---
> > >  drivers/vhost/vhost.h              |  47 ++-
> > >  drivers/vhost/vsock.c              |  42 +-
> > >  include/uapi/linux/virtio_config.h |   9 +
> > >  include/uapi/linux/virtio_ring.h   |  32 ++
> > >  7 files changed, 926 insertions(+), 226 deletions(-)
> > > 
> > > -- 
> > > 2.7.4
> > >