Commit ce10c1b9 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin

virtio: add inorder option

skips ring accesses but drops out of order support
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 2dcd0af5
all:
all: ring virtio_ring_0_9 virtio_ring_poll
all: ring virtio_ring_0_9 virtio_ring_poll virtio_ring_inorder
CFLAGS += -Wall
CFLAGS += -pthread -O2 -ggdb
......@@ -10,13 +10,16 @@ main.o: main.c main.h
ring.o: ring.c main.h
virtio_ring_0_9.o: virtio_ring_0_9.c main.h
virtio_ring_poll.o: virtio_ring_poll.c virtio_ring_0_9.c main.h
virtio_ring_inorder.o: virtio_ring_inorder.c virtio_ring_0_9.c main.h
ring: ring.o main.o
virtio_ring_0_9: virtio_ring_0_9.o main.o
virtio_ring_poll: virtio_ring_poll.o main.o
virtio_ring_inorder: virtio_ring_inorder.o main.o
clean:
-rm main.o
-rm ring.o ring
-rm virtio_ring_0_9.o virtio_ring_0_9
-rm virtio_ring_poll.o virtio_ring_poll
-rm virtio_ring_inorder.o virtio_ring_inorder
.PHONY: all clean
......@@ -26,6 +26,14 @@ struct vring ring;
* high bits of ring id ^ 0x8000).
*/
/* #ifdef RING_POLL */
/* enabling the below activates experimental in-order code
* (which skips ring updates and reads and writes len in descriptor).
*/
/* #ifdef INORDER */
#if defined(RING_POLL) && defined(INORDER)
#error "RING_POLL and INORDER are mutually exclusive"
#endif
/* how much padding is needed to avoid false cache sharing */
#define HOST_GUEST_PADDING 0x80
......@@ -35,7 +43,11 @@ struct guest {
unsigned short last_used_idx;
unsigned short num_free;
unsigned short kicked_avail_idx;
#ifndef INORDER
unsigned short free_head;
#else
unsigned short reserved_free_head;
#endif
unsigned char reserved[HOST_GUEST_PADDING - 10];
} guest;
......@@ -66,8 +78,10 @@ void alloc_ring(void)
guest.avail_idx = 0;
guest.kicked_avail_idx = -1;
guest.last_used_idx = 0;
#ifndef INORDER
/* Put everything in free lists. */
guest.free_head = 0;
#endif
for (i = 0; i < ring_size - 1; i++)
ring.desc[i].next = i + 1;
host.used_idx = 0;
......@@ -84,13 +98,20 @@ void alloc_ring(void)
/* guest side */
int add_inbuf(unsigned len, void *buf, void *datap)
{
unsigned head, avail;
unsigned head;
#ifndef INORDER
unsigned avail;
#endif
struct vring_desc *desc;
if (!guest.num_free)
return -1;
#ifdef INORDER
head = (ring_size - 1) & (guest.avail_idx++);
#else
head = guest.free_head;
#endif
guest.num_free--;
desc = ring.desc;
......@@ -102,7 +123,9 @@ int add_inbuf(unsigned len, void *buf, void *datap)
* descriptors.
*/
desc[head].flags &= ~VRING_DESC_F_NEXT;
#ifndef INORDER
guest.free_head = desc[head].next;
#endif
data[head].data = datap;
......@@ -113,8 +136,12 @@ int add_inbuf(unsigned len, void *buf, void *datap)
ring.avail->ring[avail & (ring_size - 1)] =
(head | (avail & ~(ring_size - 1))) ^ 0x8000;
#else
#ifndef INORDER
/* Barrier A (for pairing) */
smp_release();
avail = (ring_size - 1) & (guest.avail_idx++);
ring.avail->ring[avail] = head;
#endif
/* Barrier A (for pairing) */
smp_release();
#endif
......@@ -141,15 +168,27 @@ void *get_buf(unsigned *lenp, void **bufp)
return NULL;
/* Barrier B (for pairing) */
smp_acquire();
#ifdef INORDER
head = (ring_size - 1) & guest.last_used_idx;
index = head;
#else
head = (ring_size - 1) & guest.last_used_idx;
index = ring.used->ring[head].id;
#endif
#endif
#ifdef INORDER
*lenp = ring.desc[index].len;
#else
*lenp = ring.used->ring[head].len;
#endif
datap = data[index].data;
*bufp = (void*)(unsigned long)ring.desc[index].addr;
data[index].data = NULL;
#ifndef INORDER
ring.desc[index].next = guest.free_head;
guest.free_head = index;
#endif
guest.num_free++;
guest.last_used_idx++;
return datap;
......@@ -283,16 +322,24 @@ bool use_buf(unsigned *lenp, void **bufp)
smp_acquire();
used_idx &= ring_size - 1;
#ifdef INORDER
head = used_idx;
#else
head = ring.avail->ring[used_idx];
#endif
desc = &ring.desc[head];
#endif
*lenp = desc->len;
*bufp = (void *)(unsigned long)desc->addr;
#ifdef INORDER
desc->len = desc->len - 1;
#else
/* now update used ring */
ring.used->ring[used_idx].id = head;
ring.used->ring[used_idx].len = desc->len - 1;
#endif
/* Barrier B (for pairing) */
smp_release();
host.used_idx++;
......
#define INORDER 1
#include "virtio_ring_0_9.c"
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