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authorMichael S. Tsirkin <mst@redhat.com>2016-01-21 14:44:10 +0200
committerMichael S. Tsirkin <mst@redhat.com>2016-01-26 10:18:30 +0200
commit481eaec37e91e2b33f17275901172f50ce2c71e8 (patch)
treecd0df9f9f652f12820d5f615a0016da3f98839d4 /tools/virtio/ringtest
parentfb9b050ce9695cf2769a850d94aa2ab39c8c3cd5 (diff)
downloadlinux-sh-481eaec37e91e2b33f17275901172f50ce2c71e8.tar.gz
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 <mst@redhat.com>
Diffstat (limited to 'tools/virtio/ringtest')
-rw-r--r--tools/virtio/ringtest/Makefile22
-rw-r--r--tools/virtio/ringtest/README2
-rw-r--r--tools/virtio/ringtest/main.c366
-rw-r--r--tools/virtio/ringtest/main.h119
-rw-r--r--tools/virtio/ringtest/ring.c272
-rwxr-xr-xtools/virtio/ringtest/run-on-all.sh24
-rw-r--r--tools/virtio/ringtest/virtio_ring_0_9.c316
-rw-r--r--tools/virtio/ringtest/virtio_ring_poll.c2
8 files changed, 1123 insertions, 0 deletions
diff --git a/tools/virtio/ringtest/Makefile b/tools/virtio/ringtest/Makefile
new file mode 100644
index 000000000000..feaa64ac4630
--- /dev/null
+++ b/tools/virtio/ringtest/Makefile
@@ -0,0 +1,22 @@
+all:
+
+all: ring virtio_ring_0_9 virtio_ring_poll
+
+CFLAGS += -Wall
+CFLAGS += -pthread -O2 -ggdb
+LDFLAGS += -pthread -O2 -ggdb
+
+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
+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
+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
+
+.PHONY: all clean
diff --git a/tools/virtio/ringtest/README b/tools/virtio/ringtest/README
new file mode 100644
index 000000000000..34e94c46104f
--- /dev/null
+++ b/tools/virtio/ringtest/README
@@ -0,0 +1,2 @@
+Partial implementation of various ring layouts, useful to tune virtio design.
+Uses shared memory heavily.
diff --git a/tools/virtio/ringtest/main.c b/tools/virtio/ringtest/main.c
new file mode 100644
index 000000000000..3a5ff438bd62
--- /dev/null
+++ b/tools/virtio/ringtest/main.c
@@ -0,0 +1,366 @@
+/*
+ * 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.
+ *
+ * Command line processing and common functions for ring benchmarking.
+ */
+#define _GNU_SOURCE
+#include <getopt.h>
+#include <pthread.h>
+#include <assert.h>
+#include <sched.h>
+#include "main.h"
+#include <sys/eventfd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <limits.h>
+
+int runcycles = 10000000;
+int max_outstanding = INT_MAX;
+int batch = 1;
+
+bool do_sleep = false;
+bool do_relax = false;
+bool do_exit = true;
+
+unsigned ring_size = 256;
+
+static int kickfd = -1;
+static int callfd = -1;
+
+void notify(int fd)
+{
+ unsigned long long v = 1;
+ int r;
+
+ vmexit();
+ r = write(fd, &v, sizeof v);
+ assert(r == sizeof v);
+ vmentry();
+}
+
+void wait_for_notify(int fd)
+{
+ unsigned long long v = 1;
+ int r;
+
+ vmexit();
+ r = read(fd, &v, sizeof v);
+ assert(r == sizeof v);
+ vmentry();
+}
+
+void kick(void)
+{
+ notify(kickfd);
+}
+
+void wait_for_kick(void)
+{
+ wait_for_notify(kickfd);
+}
+
+void call(void)
+{
+ notify(callfd);
+}
+
+void wait_for_call(void)
+{
+ wait_for_notify(callfd);
+}
+
+void set_affinity(const char *arg)
+{
+ cpu_set_t cpuset;
+ int ret;
+ pthread_t self;
+ long int cpu;
+ char *endptr;
+
+ if (!arg)
+ return;
+
+ cpu = strtol(arg, &endptr, 0);
+ assert(!*endptr);
+
+ assert(cpu >= 0 || cpu < CPU_SETSIZE);
+
+ self = pthread_self();
+ CPU_ZERO(&cpuset);
+ CPU_SET(cpu, &cpuset);
+
+ ret = pthread_setaffinity_np(self, sizeof(cpu_set_t), &cpuset);
+ assert(!ret);
+}
+
+static void run_guest(void)
+{
+ int completed_before;
+ int completed = 0;
+ int started = 0;
+ int bufs = runcycles;
+ int spurious = 0;
+ int r;
+ unsigned len;
+ void *buf;
+ int tokick = batch;
+
+ for (;;) {
+ if (do_sleep)
+ disable_call();
+ completed_before = completed;
+ do {
+ if (started < bufs &&
+ started - completed < max_outstanding) {
+ r = add_inbuf(0, NULL, "Hello, world!");
+ if (__builtin_expect(r == 0, true)) {
+ ++started;
+ if (!--tokick) {
+ tokick = batch;
+ if (do_sleep)
+ kick_available();
+ }
+
+ }
+ } else
+ r = -1;
+
+ /* Flush out completed bufs if any */
+ if (get_buf(&len, &buf)) {
+ ++completed;
+ if (__builtin_expect(completed == bufs, false))
+ return;
+ r = 0;
+ }
+ } while (r == 0);
+ if (completed == completed_before)
+ ++spurious;
+ assert(completed <= bufs);
+ assert(started <= bufs);
+ if (do_sleep) {
+ if (enable_call())
+ wait_for_call();
+ } else {
+ poll_used();
+ }
+ }
+}
+
+static void run_host(void)
+{
+ int completed_before;
+ int completed = 0;
+ int spurious = 0;
+ int bufs = runcycles;
+ unsigned len;
+ void *buf;
+
+ for (;;) {
+ if (do_sleep) {
+ if (enable_kick())
+ wait_for_kick();
+ } else {
+ poll_avail();
+ }
+ if (do_sleep)
+ disable_kick();
+ completed_before = completed;
+ while (__builtin_expect(use_buf(&len, &buf), true)) {
+ if (do_sleep)
+ call_used();
+ ++completed;
+ if (__builtin_expect(completed == bufs, false))
+ return;
+ }
+ if (completed == completed_before)
+ ++spurious;
+ assert(completed <= bufs);
+ if (completed == bufs)
+ break;
+ }
+}
+
+void *start_guest(void *arg)
+{
+ set_affinity(arg);
+ run_guest();
+ pthread_exit(NULL);
+}
+
+void *start_host(void *arg)
+{
+ set_affinity(arg);
+ run_host();
+ pthread_exit(NULL);
+}
+
+static const char optstring[] = "";
+static const struct option longopts[] = {
+ {
+ .name = "help",
+ .has_arg = no_argument,
+ .val = 'h',
+ },
+ {
+ .name = "host-affinity",
+ .has_arg = required_argument,
+ .val = 'H',
+ },
+ {
+ .name = "guest-affinity",
+ .has_arg = required_argument,
+ .val = 'G',
+ },
+ {
+ .name = "ring-size",
+ .has_arg = required_argument,
+ .val = 'R',
+ },
+ {
+ .name = "run-cycles",
+ .has_arg = required_argument,
+ .val = 'C',
+ },
+ {
+ .name = "outstanding",
+ .has_arg = required_argument,
+ .val = 'o',
+ },
+ {
+ .name = "batch",
+ .has_arg = required_argument,
+ .val = 'b',
+ },
+ {
+ .name = "sleep",
+ .has_arg = no_argument,
+ .val = 's',
+ },
+ {
+ .name = "relax",
+ .has_arg = no_argument,
+ .val = 'x',
+ },
+ {
+ .name = "exit",
+ .has_arg = no_argument,
+ .val = 'e',
+ },
+ {
+ }
+};
+
+static void help(void)
+{
+ fprintf(stderr, "Usage: <test> [--help]"
+ " [--host-affinity H]"
+ " [--guest-affinity G]"
+ " [--ring-size R (default: %d)]"
+ " [--run-cycles C (default: %d)]"
+ " [--batch b]"
+ " [--outstanding o]"
+ " [--sleep]"
+ " [--relax]"
+ " [--exit]"
+ "\n",
+ ring_size,
+ runcycles);
+}
+
+int main(int argc, char **argv)
+{
+ int ret;
+ pthread_t host, guest;
+ void *tret;
+ char *host_arg = NULL;
+ char *guest_arg = NULL;
+ char *endptr;
+ long int c;
+
+ kickfd = eventfd(0, 0);
+ assert(kickfd >= 0);
+ callfd = eventfd(0, 0);
+ assert(callfd >= 0);
+
+ for (;;) {
+ int o = getopt_long(argc, argv, optstring, longopts, NULL);
+ switch (o) {
+ case -1:
+ goto done;
+ case '?':
+ help();
+ exit(2);
+ case 'H':
+ host_arg = optarg;
+ break;
+ case 'G':
+ guest_arg = optarg;
+ break;
+ case 'R':
+ ring_size = strtol(optarg, &endptr, 0);
+ assert(ring_size && !(ring_size & (ring_size - 1)));
+ assert(!*endptr);
+ break;
+ case 'C':
+ c = strtol(optarg, &endptr, 0);
+ assert(!*endptr);
+ assert(c > 0 && c < INT_MAX);
+ runcycles = c;
+ break;
+ case 'o':
+ c = strtol(optarg, &endptr, 0);
+ assert(!*endptr);
+ assert(c > 0 && c < INT_MAX);
+ max_outstanding = c;
+ break;
+ case 'b':
+ c = strtol(optarg, &endptr, 0);
+ assert(!*endptr);
+ assert(c > 0 && c < INT_MAX);
+ batch = c;
+ break;
+ case 's':
+ do_sleep = true;
+ break;
+ case 'x':
+ do_relax = true;
+ break;
+ case 'e':
+ do_exit = true;
+ break;
+ default:
+ help();
+ exit(4);
+ break;
+ }
+ }
+
+ /* does nothing here, used to make sure all smp APIs compile */
+ smp_acquire();
+ smp_release();
+ smp_mb();
+done:
+
+ if (batch > max_outstanding)
+ batch = max_outstanding;
+
+ if (optind < argc) {
+ help();
+ exit(4);
+ }
+ alloc_ring();
+
+ ret = pthread_create(&host, NULL, start_host, host_arg);
+ assert(!ret);
+ ret = pthread_create(&guest, NULL, start_guest, guest_arg);
+ assert(!ret);
+
+ ret = pthread_join(guest, &tret);
+ assert(!ret);
+ ret = pthread_join(host, &tret);
+ assert(!ret);
+ return 0;
+}
diff --git a/tools/virtio/ringtest/main.h b/tools/virtio/ringtest/main.h
new file mode 100644
index 000000000000..16917acb0ade
--- /dev/null
+++ b/tools/virtio/ringtest/main.h
@@ -0,0 +1,119 @@
+/*
+ * 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.
+ *
+ * Common macros and functions for ring benchmarking.
+ */
+#ifndef MAIN_H
+#define MAIN_H
+
+#include <stdbool.h>
+
+extern bool do_exit;
+
+#if defined(__x86_64__) || defined(__i386__)
+#include "x86intrin.h"
+
+static inline void wait_cycles(unsigned long long cycles)
+{
+ unsigned long long t;
+
+ t = __rdtsc();
+ while (__rdtsc() - t < cycles) {}
+}
+
+#define VMEXIT_CYCLES 500
+#define VMENTRY_CYCLES 500
+
+#else
+static inline void wait_cycles(unsigned long long cycles)
+{
+ _Exit(5);
+}
+#define VMEXIT_CYCLES 0
+#define VMENTRY_CYCLES 0
+#endif
+
+static inline void vmexit(void)
+{
+ if (!do_exit)
+ return;
+
+ wait_cycles(VMEXIT_CYCLES);
+}
+static inline void vmentry(void)
+{
+ if (!do_exit)
+ return;
+
+ wait_cycles(VMENTRY_CYCLES);
+}
+
+/* implemented by ring */
+void alloc_ring(void);
+/* guest side */
+int add_inbuf(unsigned, void *, void *);
+void *get_buf(unsigned *, void **);
+void disable_call();
+bool enable_call();
+void kick_available();
+void poll_used();
+/* host side */
+void disable_kick();
+bool enable_kick();
+bool use_buf(unsigned *, void **);
+void call_used();
+void poll_avail();
+
+/* implemented by main */
+extern bool do_sleep;
+void kick(void);
+void wait_for_kick(void);
+void call(void);
+void wait_for_call(void);
+
+extern unsigned ring_size;
+
+/* Compiler barrier - similar to what Linux uses */
+#define barrier() asm volatile("" ::: "memory")
+
+/* Is there a portable way to do this? */
+#if defined(__x86_64__) || defined(__i386__)
+#define cpu_relax() asm ("rep; nop" ::: "memory")
+#else
+#define cpu_relax() assert(0)
+#endif
+
+extern bool do_relax;
+
+static inline void busy_wait(void)
+{
+ if (do_relax)
+ cpu_relax();
+ else
+ /* prevent compiler from removing busy loops */
+ barrier();
+}
+
+/*
+ * Not using __ATOMIC_SEQ_CST since gcc docs say they are only synchronized
+ * with other __ATOMIC_SEQ_CST calls.
+ */
+#define smp_mb() __sync_synchronize()
+
+/*
+ * This abuses the atomic builtins for thread fences, and
+ * adds a compiler barrier.
+ */
+#define smp_release() do { \
+ barrier(); \
+ __atomic_thread_fence(__ATOMIC_RELEASE); \
+} while (0)
+
+#define smp_acquire() do { \
+ __atomic_thread_fence(__ATOMIC_ACQUIRE); \
+ barrier(); \
+} while (0)
+
+#endif
diff --git a/tools/virtio/ringtest/ring.c b/tools/virtio/ringtest/ring.c
new file mode 100644
index 000000000000..c25c8d248b6b
--- /dev/null
+++ b/tools/virtio/ringtest/ring.c
@@ -0,0 +1,272 @@
+/*
+ * 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.
+ *
+ * Simple descriptor-based ring. virtio 0.9 compatible event index is used for
+ * signalling, unconditionally.
+ */
+#define _GNU_SOURCE
+#include "main.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+/* Next - Where next entry will be written.
+ * Prev - "Next" value when event triggered previously.
+ * Event - Peer requested event after writing this entry.
+ */
+static inline bool need_event(unsigned short event,
+ unsigned short next,
+ unsigned short prev)
+{
+ return (unsigned short)(next - event - 1) < (unsigned short)(next - prev);
+}
+
+/* Design:
+ * Guest adds descriptors with unique index values and DESC_HW in flags.
+ * Host overwrites used descriptors with correct len, index, and DESC_HW clear.
+ * Flags are always set last.
+ */
+#define DESC_HW 0x1
+
+struct desc {
+ unsigned short flags;
+ unsigned short index;
+ unsigned len;
+ unsigned long long addr;
+};
+
+/* how much padding is needed to avoid false cache sharing */
+#define HOST_GUEST_PADDING 0x80
+
+/* Mostly read */
+struct event {
+ unsigned short kick_index;
+ unsigned char reserved0[HOST_GUEST_PADDING - 2];
+ unsigned short call_index;
+ unsigned char reserved1[HOST_GUEST_PADDING - 2];
+};
+
+struct data {
+ void *buf; /* descriptor is writeable, we can't get buf from there */
+ void *data;
+} *data;
+
+struct desc *ring;
+struct event *event;
+
+struct guest {
+ unsigned avail_idx;
+ unsigned last_used_idx;
+ unsigned num_free;
+ unsigned kicked_avail_idx;
+ unsigned char reserved[HOST_GUEST_PADDING - 12];
+} guest;
+
+struct host {
+ /* we do not need to track last avail index
+ * unless we have more than one in flight.
+ */
+ unsigned used_idx;
+ unsigned called_used_idx;
+ unsigned char reserved[HOST_GUEST_PADDING - 4];
+} host;
+
+/* implemented by ring */
+void alloc_ring(void)
+{
+ int ret;
+ int i;
+
+ ret = posix_memalign((void **)&ring, 0x1000, ring_size * sizeof *ring);
+ if (ret) {
+ perror("Unable to allocate ring buffer.\n");
+ exit(3);
+ }
+ event = malloc(sizeof *event);
+ if (!event) {
+ perror("Unable to allocate event buffer.\n");
+ exit(3);
+ }
+ memset(event, 0, sizeof *event);
+ guest.avail_idx = 0;
+ guest.kicked_avail_idx = -1;
+ guest.last_used_idx = 0;
+ host.used_idx = 0;
+ host.called_used_idx = -1;
+ for (i = 0; i < ring_size; ++i) {
+ struct desc desc = {
+ .index = i,
+ };
+ ring[i] = desc;
+ }
+ 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, index;
+
+ if (!guest.num_free)
+ return -1;
+
+ guest.num_free--;
+ head = (ring_size - 1) & (guest.avail_idx++);
+
+ /* Start with a write. On MESI architectures this helps
+ * avoid a shared state with consumer that is polling this descriptor.
+ */
+ ring[head].addr = (unsigned long)(void*)buf;
+ ring[head].len = len;
+ /* read below might bypass write above. That is OK because it's just an
+ * optimization. If this happens, we will get the cache line in a
+ * shared state which is unfortunate, but probably not worth it to
+ * add an explicit full barrier to avoid this.
+ */
+ barrier();
+ index = ring[head].index;
+ data[index].buf = buf;
+ data[index].data = datap;
+ /* Barrier A (for pairing) */
+ smp_release();
+ ring[head].flags = DESC_HW;
+
+ return 0;
+}
+
+void *get_buf(unsigned *lenp, void **bufp)
+{
+ unsigned head = (ring_size - 1) & guest.last_used_idx;
+ unsigned index;
+ void *datap;
+
+ if (ring[head].flags & DESC_HW)
+ return NULL;
+ /* Barrier B (for pairing) */
+ smp_acquire();
+ *lenp = ring[head].len;
+ index = ring[head].index & (ring_size - 1);
+ datap = data[index].data;
+ *bufp = data[index].buf;
+ data[index].buf = NULL;
+ data[index].data = NULL;
+ guest.num_free++;
+ guest.last_used_idx++;
+ return datap;
+}
+
+void poll_used(void)
+{
+ unsigned head = (ring_size - 1) & guest.last_used_idx;
+
+ while (ring[head].flags & DESC_HW)
+ busy_wait();
+}
+
+void disable_call()
+{
+ /* Doing nothing to disable calls might cause
+ * extra interrupts, but reduces the number of cache misses.
+ */
+}
+
+bool enable_call()
+{
+ unsigned head = (ring_size - 1) & guest.last_used_idx;
+
+ event->call_index = guest.last_used_idx;
+ /* Flush call index write */
+ /* Barrier D (for pairing) */
+ smp_mb();
+ return ring[head].flags & DESC_HW;
+}
+
+void kick_available(void)
+{
+ /* Flush in previous flags write */
+ /* Barrier C (for pairing) */
+ smp_mb();
+ if (!need_event(event->kick_index,
+ 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 = (ring_size - 1) & host.used_idx;
+
+ event->kick_index = host.used_idx;
+ /* Barrier C (for pairing) */
+ smp_mb();
+ return !(ring[head].flags & DESC_HW);
+}
+
+void poll_avail(void)
+{
+ unsigned head = (ring_size - 1) & host.used_idx;
+
+ while (!(ring[head].flags & DESC_HW))
+ busy_wait();
+}
+
+bool use_buf(unsigned *lenp, void **bufp)
+{
+ unsigned head = (ring_size - 1) & host.used_idx;
+
+ if (!(ring[head].flags & DESC_HW))
+ return false;
+
+ /* make sure length read below is not speculated */
+ /* Barrier A (for pairing) */
+ smp_acquire();
+
+ /* simple in-order completion: we don't need
+ * to touch index at all. This also means we
+ * can just modify the descriptor in-place.
+ */
+ ring[head].len--;
+ /* Make sure len is valid before flags.
+ * Note: alternative is to write len and flags in one access -
+ * possible on 64 bit architectures but wmb is free on Intel anyway
+ * so I have no way to test whether it's a gain.
+ */
+ /* Barrier B (for pairing) */
+ smp_release();
+ ring[head].flags = 0;
+ host.used_idx++;
+ return true;
+}
+
+void call_used(void)
+{
+ /* Flush in previous flags write */
+ /* Barrier D (for pairing) */
+ smp_mb();
+ if (!need_event(event->call_index,
+ host.used_idx,
+ host.called_used_idx))
+ return;
+
+ host.called_used_idx = host.used_idx;
+ call();
+}
diff --git a/tools/virtio/ringtest/run-on-all.sh b/tools/virtio/ringtest/run-on-all.sh
new file mode 100755
index 000000000000..52b0f71ffa8d
--- /dev/null
+++ b/tools/virtio/ringtest/run-on-all.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+#use last CPU for host. Why not the first?
+#many devices tend to use cpu0 by default so
+#it tends to be busier
+HOST_AFFINITY=$(cd /dev/cpu; ls|grep -v '[a-z]'|sort -n|tail -1)
+
+#run command on all cpus
+for cpu in $(cd /dev/cpu; ls|grep -v '[a-z]'|sort -n);
+do
+ #Don't run guest and host on same CPU
+ #It actually works ok if using signalling
+ if
+ (echo "$@" | grep -e "--sleep" > /dev/null) || \
+ test $HOST_AFFINITY '!=' $cpu
+ then
+ echo "GUEST AFFINITY $cpu"
+ "$@" --host-affinity $HOST_AFFINITY --guest-affinity $cpu
+ fi
+done
+echo "NO GUEST AFFINITY"
+"$@" --host-affinity $HOST_AFFINITY
+echo "NO AFFINITY"
+"$@"
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 <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();
+}
diff --git a/tools/virtio/ringtest/virtio_ring_poll.c b/tools/virtio/ringtest/virtio_ring_poll.c
new file mode 100644
index 000000000000..84fc2c557aaa
--- /dev/null
+++ b/tools/virtio/ringtest/virtio_ring_poll.c
@@ -0,0 +1,2 @@
+#define RING_POLL 1
+#include "virtio_ring_0_9.c"