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Message-ID: <5113AA35.3010209@redhat.com> Date: Thu, 07 Feb 2013 14:20:53 +0100 From: Paolo Bonzini <pbonzini@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com> CC: linux-kernel@...r.kernel.org, Wanlong Gao <gaowanlong@...fujitsu.com>, asias@...hat.com, Rusty Russell <rusty@...tcorp.com.au>, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org Subject: Re: [RFC PATCH 0/8] virtio: new API for addition of buffers, scatterlist changes Il 07/02/2013 14:23, Michael S. Tsirkin ha scritto: > On Thu, Feb 07, 2013 at 02:14:24PM +0100, Paolo Bonzini wrote: >> Il 07/02/2013 14:09, Michael S. Tsirkin ha scritto: >>>> One major difference between virtqueue_add_buf and virtqueue_add_sg >>>> is that the latter uses scatterlist iterators, which follow chained >>>> scatterlist structs and stop at ending markers. In order to avoid code >>>> duplication, and use the new API from virtqueue_add_buf (patch 8), we need >>>> to change all existing callers of virtqueue_add_buf to provide well-formed >>>> scatterlists. This is what patches 2-7 do. For virtio-blk it is easiest >>>> to just switch to the new API, just like for virtio-scsi. For virtio-net >>>> the ending marker must be reset after calling virtqueue_add_buf, in >>>> preparation for the next usage of the scatterlist. Other drivers are >>>> safe already. >>> >>> What are the changes as compared to the previous version? >>> How about some comments made on the previous version? >>> See e.g. >>> https://patchwork.kernel.org/patch/1891541/ >> >> Two changes: 1) added virtqueue_add_sg_single; 2) reimplemented >> virtqueue_add_buf in terms of the new API, which requires virtio-blk and >> virtio-net changes. >> >> The virtio-blk and virtio-net changes are based on some ideas in the >> patch Rusty posted, but virtio-net is a bit simpler and virtio-blk was >> redone from scratch. >> >>> Generally we have code for direct and indirect which is already >>> painful. We do not want 4 more variants of this code. >> >> Yes, indeed, the other main difference is that I'm now reimplementing >> virtqueue_add_buf using the new functions. So: >> >> - we previously had 2 variants (direct/indirect) >> >> - v1 had 4 variants (direct/indirect x add_buf/add_sg) >> >> - v2 has 4 variants (direct/indirect x add_sg/add_sg_single) > > single is never indirect so should have a single variant. Single means *this piece* (for example a request header) is single. It could still end up in an indirect buffer because QEMU does not support mixed direct/indirect buffers. Paolo >>>> This is an RFC for two reasons. First, because I haven't done enough >>>> testing yet (especially with all the variations on receiving that >>>> virtio-net has). Second, because I still have two struct vring_desc * >>>> fields in virtqueue API, which is a layering violation. I'm not really >>>> sure how important that is and how to fix that---except by making the >>>> fields void*. >>> >>> Hide the whole structure as part of vring struct, the problem will go >>> away. >> >> Yes, that's the other possibility. Will do for the next submission. >> >> Paolo >> >>>> Paolo >>>> Paolo Bonzini (8): >>>> virtio: add functions for piecewise addition of buffers >>>> virtio-blk: reorganize virtblk_add_req >>>> virtio-blk: use virtqueue_start_buf on bio path >>>> virtio-blk: use virtqueue_start_buf on req path >>>> scatterlist: introduce sg_unmark_end >>>> virtio-net: unmark scatterlist ending after virtqueue_add_buf >>>> virtio-scsi: use virtqueue_start_buf >>>> virtio: reimplement virtqueue_add_buf using new functions >>>> >>>> block/blk-integrity.c | 2 +- >>>> block/blk-merge.c | 2 +- >>>> drivers/block/virtio_blk.c | 165 +++++++++-------- >>>> drivers/net/virtio_net.c | 21 ++- >>>> drivers/scsi/virtio_scsi.c | 103 +++++------ >>>> drivers/virtio/virtio_ring.c | 417 +++++++++++++++++++++++++++--------------- >>>> include/linux/scatterlist.h | 16 ++ >>>> include/linux/virtio.h | 25 +++ >>>> 8 files changed, 460 insertions(+), 291 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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