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7b21e34fd1
We were cheating with our barriers; using the smp ones rather than the
real device ones. That was fine, until rpmsg came along, which is
used to talk to a real device (a non-SMP CPU).
Unfortunately, just putting back the real barriers (reverting
d57ed95d) causes a performance regression on virtio-pci. In
particular, Amos reports netbench's TCP_RR over virtio_net CPU
utilization increased up to 35% while throughput went down by up to
14%.
By comparison, this branch is in the noise.
Reference: https://lkml.org/lkml/2011/12/11/22
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
183 lines
6.4 KiB
C
183 lines
6.4 KiB
C
#ifndef _LINUX_VIRTIO_RING_H
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#define _LINUX_VIRTIO_RING_H
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/* An interface for efficient virtio implementation, currently for use by KVM
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* and lguest, but hopefully others soon. Do NOT change this since it will
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* break existing servers and clients.
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*
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* This header is BSD licensed so anyone can use the definitions to implement
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* compatible drivers/servers.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of IBM nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL IBM OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* Copyright Rusty Russell IBM Corporation 2007. */
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#include <linux/types.h>
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/* This marks a buffer as continuing via the next field. */
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#define VRING_DESC_F_NEXT 1
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/* This marks a buffer as write-only (otherwise read-only). */
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#define VRING_DESC_F_WRITE 2
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/* This means the buffer contains a list of buffer descriptors. */
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#define VRING_DESC_F_INDIRECT 4
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/* The Host uses this in used->flags to advise the Guest: don't kick me when
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* you add a buffer. It's unreliable, so it's simply an optimization. Guest
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* will still kick if it's out of buffers. */
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#define VRING_USED_F_NO_NOTIFY 1
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/* The Guest uses this in avail->flags to advise the Host: don't interrupt me
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* when you consume a buffer. It's unreliable, so it's simply an
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* optimization. */
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#define VRING_AVAIL_F_NO_INTERRUPT 1
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/* We support indirect buffer descriptors */
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#define VIRTIO_RING_F_INDIRECT_DESC 28
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/* The Guest publishes the used index for which it expects an interrupt
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* at the end of the avail ring. Host should ignore the avail->flags field. */
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/* The Host publishes the avail index for which it expects a kick
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* at the end of the used ring. Guest should ignore the used->flags field. */
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#define VIRTIO_RING_F_EVENT_IDX 29
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/* Virtio ring descriptors: 16 bytes. These can chain together via "next". */
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struct vring_desc {
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/* Address (guest-physical). */
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__u64 addr;
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/* Length. */
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__u32 len;
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/* The flags as indicated above. */
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__u16 flags;
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/* We chain unused descriptors via this, too */
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__u16 next;
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};
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struct vring_avail {
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__u16 flags;
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__u16 idx;
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__u16 ring[];
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};
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/* u32 is used here for ids for padding reasons. */
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struct vring_used_elem {
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/* Index of start of used descriptor chain. */
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__u32 id;
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/* Total length of the descriptor chain which was used (written to) */
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__u32 len;
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};
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struct vring_used {
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__u16 flags;
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__u16 idx;
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struct vring_used_elem ring[];
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};
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struct vring {
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unsigned int num;
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struct vring_desc *desc;
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struct vring_avail *avail;
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struct vring_used *used;
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};
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/* The standard layout for the ring is a continuous chunk of memory which looks
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* like this. We assume num is a power of 2.
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*
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* struct vring
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* {
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* // The actual descriptors (16 bytes each)
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* struct vring_desc desc[num];
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*
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* // A ring of available descriptor heads with free-running index.
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* __u16 avail_flags;
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* __u16 avail_idx;
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* __u16 available[num];
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* __u16 used_event_idx;
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*
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* // Padding to the next align boundary.
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* char pad[];
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*
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* // A ring of used descriptor heads with free-running index.
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* __u16 used_flags;
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* __u16 used_idx;
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* struct vring_used_elem used[num];
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* __u16 avail_event_idx;
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* };
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*/
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/* We publish the used event index at the end of the available ring, and vice
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* versa. They are at the end for backwards compatibility. */
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#define vring_used_event(vr) ((vr)->avail->ring[(vr)->num])
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#define vring_avail_event(vr) (*(__u16 *)&(vr)->used->ring[(vr)->num])
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static inline void vring_init(struct vring *vr, unsigned int num, void *p,
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unsigned long align)
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{
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vr->num = num;
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vr->desc = p;
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vr->avail = p + num*sizeof(struct vring_desc);
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vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__u16)
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+ align-1) & ~(align - 1));
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}
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static inline unsigned vring_size(unsigned int num, unsigned long align)
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{
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return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
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+ align - 1) & ~(align - 1))
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+ sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
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}
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/* The following is used with USED_EVENT_IDX and AVAIL_EVENT_IDX */
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/* Assuming a given event_idx value from the other size, if
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* we have just incremented index from old to new_idx,
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* should we trigger an event? */
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static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
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{
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/* Note: Xen has similar logic for notification hold-off
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* in include/xen/interface/io/ring.h with req_event and req_prod
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* corresponding to event_idx + 1 and new_idx respectively.
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* Note also that req_event and req_prod in Xen start at 1,
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* event indexes in virtio start at 0. */
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return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
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}
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#ifdef __KERNEL__
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#include <linux/irqreturn.h>
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struct virtio_device;
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struct virtqueue;
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struct virtqueue *vring_new_virtqueue(unsigned int num,
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unsigned int vring_align,
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struct virtio_device *vdev,
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bool weak_barriers,
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void *pages,
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void (*notify)(struct virtqueue *vq),
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void (*callback)(struct virtqueue *vq),
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const char *name);
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void vring_del_virtqueue(struct virtqueue *vq);
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/* Filter out transport-specific feature bits. */
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void vring_transport_features(struct virtio_device *vdev);
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irqreturn_t vring_interrupt(int irq, void *_vq);
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#endif /* __KERNEL__ */
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#endif /* _LINUX_VIRTIO_RING_H */
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