From 481eaec37e91e2b33f17275901172f50ce2c71e8 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Thu, 21 Jan 2016 14:44:10 +0200 Subject: tools/virtio: add ringtest utilities This adds micro-benchmarks useful for tuning virtio ring layouts. Three layouts are currently implemented: - virtio 0.9 compatible one - an experimental extension bypassing the ring index, polling ring itself instead - an experimental extension bypassing avail and used ring completely Typical use: sh run-on-all.sh perf stat -r 10 --log-fd 1 -- ./ring It doesn't depend on the kernel directly, but it's handy to have as much virtio stuff as possible in one tree. Signed-off-by: Michael S. Tsirkin --- tools/virtio/ringtest/virtio_ring_0_9.c | 316 ++++++++++++++++++++++++++++++++ 1 file changed, 316 insertions(+) create mode 100644 tools/virtio/ringtest/virtio_ring_0_9.c (limited to 'tools/virtio/ringtest/virtio_ring_0_9.c') diff --git a/tools/virtio/ringtest/virtio_ring_0_9.c b/tools/virtio/ringtest/virtio_ring_0_9.c new file mode 100644 index 000000000000..47c9a1a18d36 --- /dev/null +++ b/tools/virtio/ringtest/virtio_ring_0_9.c @@ -0,0 +1,316 @@ +/* + * Copyright (C) 2016 Red Hat, Inc. + * Author: Michael S. Tsirkin + * 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 +#include +#include +#include +#include + +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(); +} -- cgit v1.2.3