--- /dev/null
+/*
+ * Copyright (C) 2016 Red Hat, Inc.
+ * Author: Michael S. Tsirkin <mst@redhat.com>
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * Partial implementation of virtio 0.9. event index is used for signalling,
+ * unconditionally. Design roughly follows linux kernel implementation in order
+ * to be able to judge its performance.
+ */
+#define _GNU_SOURCE
+#include "main.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <assert.h>
+#include <string.h>
+#include <linux/virtio_ring.h>
+
+struct data {
+ void *data;
+} *data;
+
+struct vring ring;
+
+/* enabling the below activates experimental ring polling code
+ * (which skips index reads on consumer in favor of looking at
+ * high bits of ring id ^ 0x8000).
+ */
+/* #ifdef RING_POLL */
+
+/* how much padding is needed to avoid false cache sharing */
+#define HOST_GUEST_PADDING 0x80
+
+struct guest {
+ unsigned short avail_idx;
+ unsigned short last_used_idx;
+ unsigned short num_free;
+ unsigned short kicked_avail_idx;
+ unsigned short free_head;
+ unsigned char reserved[HOST_GUEST_PADDING - 10];
+} guest;
+
+struct host {
+ /* we do not need to track last avail index
+ * unless we have more than one in flight.
+ */
+ unsigned short used_idx;
+ unsigned short called_used_idx;
+ unsigned char reserved[HOST_GUEST_PADDING - 4];
+} host;
+
+/* implemented by ring */
+void alloc_ring(void)
+{
+ int ret;
+ int i;
+ void *p;
+
+ ret = posix_memalign(&p, 0x1000, vring_size(ring_size, 0x1000));
+ if (ret) {
+ perror("Unable to allocate ring buffer.\n");
+ exit(3);
+ }
+ memset(p, 0, vring_size(ring_size, 0x1000));
+ vring_init(&ring, ring_size, p, 0x1000);
+
+ guest.avail_idx = 0;
+ guest.kicked_avail_idx = -1;
+ guest.last_used_idx = 0;
+ /* Put everything in free lists. */
+ guest.free_head = 0;
+ for (i = 0; i < ring_size - 1; i++)
+ ring.desc[i].next = i + 1;
+ host.used_idx = 0;
+ host.called_used_idx = -1;
+ guest.num_free = ring_size;
+ data = malloc(ring_size * sizeof *data);
+ if (!data) {
+ perror("Unable to allocate data buffer.\n");
+ exit(3);
+ }
+ memset(data, 0, ring_size * sizeof *data);
+}
+
+/* guest side */
+int add_inbuf(unsigned len, void *buf, void *datap)
+{
+ unsigned head, avail;
+ struct vring_desc *desc;
+
+ if (!guest.num_free)
+ return -1;
+
+ head = guest.free_head;
+ guest.num_free--;
+
+ desc = ring.desc;
+ desc[head].flags = VRING_DESC_F_NEXT;
+ desc[head].addr = (unsigned long)(void *)buf;
+ desc[head].len = len;
+ /* We do it like this to simulate the way
+ * we'd have to flip it if we had multiple
+ * descriptors.
+ */
+ desc[head].flags &= ~VRING_DESC_F_NEXT;
+ guest.free_head = desc[head].next;
+
+ data[head].data = datap;
+
+#ifdef RING_POLL
+ /* Barrier A (for pairing) */
+ smp_release();
+ avail = guest.avail_idx++;
+ ring.avail->ring[avail & (ring_size - 1)] =
+ (head | (avail & ~(ring_size - 1))) ^ 0x8000;
+#else
+ avail = (ring_size - 1) & (guest.avail_idx++);
+ ring.avail->ring[avail] = head;
+ /* Barrier A (for pairing) */
+ smp_release();
+#endif
+ ring.avail->idx = guest.avail_idx;
+ return 0;
+}
+
+void *get_buf(unsigned *lenp, void **bufp)
+{
+ unsigned head;
+ unsigned index;
+ void *datap;
+
+#ifdef RING_POLL
+ head = (ring_size - 1) & guest.last_used_idx;
+ index = ring.used->ring[head].id;
+ if ((index ^ guest.last_used_idx ^ 0x8000) & ~(ring_size - 1))
+ return NULL;
+ /* Barrier B (for pairing) */
+ smp_acquire();
+ index &= ring_size - 1;
+#else
+ if (ring.used->idx == guest.last_used_idx)
+ return NULL;
+ /* Barrier B (for pairing) */
+ smp_acquire();
+ head = (ring_size - 1) & guest.last_used_idx;
+ index = ring.used->ring[head].id;
+#endif
+ *lenp = ring.used->ring[head].len;
+ datap = data[index].data;
+ *bufp = (void*)(unsigned long)ring.desc[index].addr;
+ data[index].data = NULL;
+ ring.desc[index].next = guest.free_head;
+ guest.free_head = index;
+ guest.num_free++;
+ guest.last_used_idx++;
+ return datap;
+}
+
+void poll_used(void)
+{
+#ifdef RING_POLL
+ unsigned head = (ring_size - 1) & guest.last_used_idx;
+
+ for (;;) {
+ unsigned index = ring.used->ring[head].id;
+
+ if ((index ^ guest.last_used_idx ^ 0x8000) & ~(ring_size - 1))
+ busy_wait();
+ else
+ break;
+ }
+#else
+ unsigned head = guest.last_used_idx;
+
+ while (ring.used->idx == head)
+ busy_wait();
+#endif
+}
+
+void disable_call()
+{
+ /* Doing nothing to disable calls might cause
+ * extra interrupts, but reduces the number of cache misses.
+ */
+}
+
+bool enable_call()
+{
+ unsigned short last_used_idx;
+
+ vring_used_event(&ring) = (last_used_idx = guest.last_used_idx);
+ /* Flush call index write */
+ /* Barrier D (for pairing) */
+ smp_mb();
+#ifdef RING_POLL
+ {
+ unsigned short head = last_used_idx & (ring_size - 1);
+ unsigned index = ring.used->ring[head].id;
+
+ return (index ^ last_used_idx ^ 0x8000) & ~(ring_size - 1);
+ }
+#else
+ return ring.used->idx == last_used_idx;
+#endif
+}
+
+void kick_available(void)
+{
+ /* Flush in previous flags write */
+ /* Barrier C (for pairing) */
+ smp_mb();
+ if (!vring_need_event(vring_avail_event(&ring),
+ guest.avail_idx,
+ guest.kicked_avail_idx))
+ return;
+
+ guest.kicked_avail_idx = guest.avail_idx;
+ kick();
+}
+
+/* host side */
+void disable_kick()
+{
+ /* Doing nothing to disable kicks might cause
+ * extra interrupts, but reduces the number of cache misses.
+ */
+}
+
+bool enable_kick()
+{
+ unsigned head = host.used_idx;
+
+ vring_avail_event(&ring) = head;
+ /* Barrier C (for pairing) */
+ smp_mb();
+#ifdef RING_POLL
+ {
+ unsigned index = ring.avail->ring[head & (ring_size - 1)];
+
+ return (index ^ head ^ 0x8000) & ~(ring_size - 1);
+ }
+#else
+ return head == ring.avail->idx;
+#endif
+}
+
+void poll_avail(void)
+{
+ unsigned head = host.used_idx;
+#ifdef RING_POLL
+ for (;;) {
+ unsigned index = ring.avail->ring[head & (ring_size - 1)];
+ if ((index ^ head ^ 0x8000) & ~(ring_size - 1))
+ busy_wait();
+ else
+ break;
+ }
+#else
+ while (ring.avail->idx == head)
+ busy_wait();
+#endif
+}
+
+bool use_buf(unsigned *lenp, void **bufp)
+{
+ unsigned used_idx = host.used_idx;
+ struct vring_desc *desc;
+ unsigned head;
+
+#ifdef RING_POLL
+ head = ring.avail->ring[used_idx & (ring_size - 1)];
+ if ((used_idx ^ head ^ 0x8000) & ~(ring_size - 1))
+ return false;
+ /* Barrier A (for pairing) */
+ smp_acquire();
+
+ used_idx &= ring_size - 1;
+ desc = &ring.desc[head & (ring_size - 1)];
+#else
+ if (used_idx == ring.avail->idx)
+ return false;
+
+ /* Barrier A (for pairing) */
+ smp_acquire();
+
+ used_idx &= ring_size - 1;
+ head = ring.avail->ring[used_idx];
+ desc = &ring.desc[head];
+#endif
+
+ *lenp = desc->len;
+ *bufp = (void *)(unsigned long)desc->addr;
+
+ /* now update used ring */
+ ring.used->ring[used_idx].id = head;
+ ring.used->ring[used_idx].len = desc->len - 1;
+ /* Barrier B (for pairing) */
+ smp_release();
+ host.used_idx++;
+ ring.used->idx = host.used_idx;
+
+ return true;
+}
+
+void call_used(void)
+{
+ /* Flush in previous flags write */
+ /* Barrier D (for pairing) */
+ smp_mb();
+ if (!vring_need_event(vring_used_event(&ring),
+ host.used_idx,
+ host.called_used_idx))
+ return;
+
+ host.called_used_idx = host.used_idx;
+ call();
+}
projects / cascardo / linux.git / blobdiff