qemu/aio-posix.c

758 lines
20 KiB
C

/*
* QEMU aio implementation
*
* Copyright IBM, Corp. 2008
*
* Authors:
* Anthony Liguori <aliguori@us.ibm.com>
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
* Contributions after 2012-01-13 are licensed under the terms of the
* GNU GPL, version 2 or (at your option) any later version.
*/
#include "qemu/osdep.h"
#include "qemu-common.h"
#include "block/block.h"
#include "qemu/rcu_queue.h"
#include "qemu/sockets.h"
#include "qemu/cutils.h"
#include "trace.h"
#ifdef CONFIG_EPOLL_CREATE1
#include <sys/epoll.h>
#endif
struct AioHandler
{
GPollFD pfd;
IOHandler *io_read;
IOHandler *io_write;
AioPollFn *io_poll;
IOHandler *io_poll_begin;
IOHandler *io_poll_end;
int deleted;
void *opaque;
bool is_external;
QLIST_ENTRY(AioHandler) node;
};
#ifdef CONFIG_EPOLL_CREATE1
/* The fd number threashold to switch to epoll */
#define EPOLL_ENABLE_THRESHOLD 64
static void aio_epoll_disable(AioContext *ctx)
{
ctx->epoll_available = false;
if (!ctx->epoll_enabled) {
return;
}
ctx->epoll_enabled = false;
close(ctx->epollfd);
}
static inline int epoll_events_from_pfd(int pfd_events)
{
return (pfd_events & G_IO_IN ? EPOLLIN : 0) |
(pfd_events & G_IO_OUT ? EPOLLOUT : 0) |
(pfd_events & G_IO_HUP ? EPOLLHUP : 0) |
(pfd_events & G_IO_ERR ? EPOLLERR : 0);
}
static bool aio_epoll_try_enable(AioContext *ctx)
{
AioHandler *node;
struct epoll_event event;
QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
int r;
if (node->deleted || !node->pfd.events) {
continue;
}
event.events = epoll_events_from_pfd(node->pfd.events);
event.data.ptr = node;
r = epoll_ctl(ctx->epollfd, EPOLL_CTL_ADD, node->pfd.fd, &event);
if (r) {
return false;
}
}
ctx->epoll_enabled = true;
return true;
}
static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
{
struct epoll_event event;
int r;
int ctl;
if (!ctx->epoll_enabled) {
return;
}
if (!node->pfd.events) {
ctl = EPOLL_CTL_DEL;
} else {
event.data.ptr = node;
event.events = epoll_events_from_pfd(node->pfd.events);
ctl = is_new ? EPOLL_CTL_ADD : EPOLL_CTL_MOD;
}
r = epoll_ctl(ctx->epollfd, ctl, node->pfd.fd, &event);
if (r) {
aio_epoll_disable(ctx);
}
}
static int aio_epoll(AioContext *ctx, GPollFD *pfds,
unsigned npfd, int64_t timeout)
{
AioHandler *node;
int i, ret = 0;
struct epoll_event events[128];
assert(npfd == 1);
assert(pfds[0].fd == ctx->epollfd);
if (timeout > 0) {
ret = qemu_poll_ns(pfds, npfd, timeout);
}
if (timeout <= 0 || ret > 0) {
ret = epoll_wait(ctx->epollfd, events,
sizeof(events) / sizeof(events[0]),
timeout);
if (ret <= 0) {
goto out;
}
for (i = 0; i < ret; i++) {
int ev = events[i].events;
node = events[i].data.ptr;
node->pfd.revents = (ev & EPOLLIN ? G_IO_IN : 0) |
(ev & EPOLLOUT ? G_IO_OUT : 0) |
(ev & EPOLLHUP ? G_IO_HUP : 0) |
(ev & EPOLLERR ? G_IO_ERR : 0);
}
}
out:
return ret;
}
static bool aio_epoll_enabled(AioContext *ctx)
{
/* Fall back to ppoll when external clients are disabled. */
return !aio_external_disabled(ctx) && ctx->epoll_enabled;
}
static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
unsigned npfd, int64_t timeout)
{
if (!ctx->epoll_available) {
return false;
}
if (aio_epoll_enabled(ctx)) {
return true;
}
if (npfd >= EPOLL_ENABLE_THRESHOLD) {
if (aio_epoll_try_enable(ctx)) {
return true;
} else {
aio_epoll_disable(ctx);
}
}
return false;
}
#else
static void aio_epoll_update(AioContext *ctx, AioHandler *node, bool is_new)
{
}
static int aio_epoll(AioContext *ctx, GPollFD *pfds,
unsigned npfd, int64_t timeout)
{
assert(false);
}
static bool aio_epoll_enabled(AioContext *ctx)
{
return false;
}
static bool aio_epoll_check_poll(AioContext *ctx, GPollFD *pfds,
unsigned npfd, int64_t timeout)
{
return false;
}
#endif
static AioHandler *find_aio_handler(AioContext *ctx, int fd)
{
AioHandler *node;
QLIST_FOREACH(node, &ctx->aio_handlers, node) {
if (node->pfd.fd == fd)
if (!node->deleted)
return node;
}
return NULL;
}
void aio_set_fd_handler(AioContext *ctx,
int fd,
bool is_external,
IOHandler *io_read,
IOHandler *io_write,
AioPollFn *io_poll,
void *opaque)
{
AioHandler *node;
bool is_new = false;
bool deleted = false;
qemu_lockcnt_lock(&ctx->list_lock);
node = find_aio_handler(ctx, fd);
/* Are we deleting the fd handler? */
if (!io_read && !io_write && !io_poll) {
if (node == NULL) {
qemu_lockcnt_unlock(&ctx->list_lock);
return;
}
g_source_remove_poll(&ctx->source, &node->pfd);
/* If the lock is held, just mark the node as deleted */
if (qemu_lockcnt_count(&ctx->list_lock)) {
node->deleted = 1;
node->pfd.revents = 0;
} else {
/* Otherwise, delete it for real. We can't just mark it as
* deleted because deleted nodes are only cleaned up while
* no one is walking the handlers list.
*/
QLIST_REMOVE(node, node);
deleted = true;
}
if (!node->io_poll) {
ctx->poll_disable_cnt--;
}
} else {
if (node == NULL) {
/* Alloc and insert if it's not already there */
node = g_new0(AioHandler, 1);
node->pfd.fd = fd;
QLIST_INSERT_HEAD_RCU(&ctx->aio_handlers, node, node);
g_source_add_poll(&ctx->source, &node->pfd);
is_new = true;
ctx->poll_disable_cnt += !io_poll;
} else {
ctx->poll_disable_cnt += !io_poll - !node->io_poll;
}
/* Update handler with latest information */
node->io_read = io_read;
node->io_write = io_write;
node->io_poll = io_poll;
node->opaque = opaque;
node->is_external = is_external;
node->pfd.events = (io_read ? G_IO_IN | G_IO_HUP | G_IO_ERR : 0);
node->pfd.events |= (io_write ? G_IO_OUT | G_IO_ERR : 0);
}
aio_epoll_update(ctx, node, is_new);
qemu_lockcnt_unlock(&ctx->list_lock);
aio_notify(ctx);
if (deleted) {
g_free(node);
}
}
void aio_set_fd_poll(AioContext *ctx, int fd,
IOHandler *io_poll_begin,
IOHandler *io_poll_end)
{
AioHandler *node = find_aio_handler(ctx, fd);
if (!node) {
return;
}
node->io_poll_begin = io_poll_begin;
node->io_poll_end = io_poll_end;
}
void aio_set_event_notifier(AioContext *ctx,
EventNotifier *notifier,
bool is_external,
EventNotifierHandler *io_read,
AioPollFn *io_poll)
{
aio_set_fd_handler(ctx, event_notifier_get_fd(notifier), is_external,
(IOHandler *)io_read, NULL, io_poll, notifier);
}
void aio_set_event_notifier_poll(AioContext *ctx,
EventNotifier *notifier,
EventNotifierHandler *io_poll_begin,
EventNotifierHandler *io_poll_end)
{
aio_set_fd_poll(ctx, event_notifier_get_fd(notifier),
(IOHandler *)io_poll_begin,
(IOHandler *)io_poll_end);
}
static void poll_set_started(AioContext *ctx, bool started)
{
AioHandler *node;
if (started == ctx->poll_started) {
return;
}
ctx->poll_started = started;
qemu_lockcnt_inc(&ctx->list_lock);
QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
IOHandler *fn;
if (node->deleted) {
continue;
}
if (started) {
fn = node->io_poll_begin;
} else {
fn = node->io_poll_end;
}
if (fn) {
fn(node->opaque);
}
}
qemu_lockcnt_dec(&ctx->list_lock);
}
bool aio_prepare(AioContext *ctx)
{
/* Poll mode cannot be used with glib's event loop, disable it. */
poll_set_started(ctx, false);
return false;
}
bool aio_pending(AioContext *ctx)
{
AioHandler *node;
bool result = false;
/*
* We have to walk very carefully in case aio_set_fd_handler is
* called while we're walking.
*/
qemu_lockcnt_inc(&ctx->list_lock);
QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
int revents;
revents = node->pfd.revents & node->pfd.events;
if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read &&
aio_node_check(ctx, node->is_external)) {
result = true;
break;
}
if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write &&
aio_node_check(ctx, node->is_external)) {
result = true;
break;
}
}
qemu_lockcnt_dec(&ctx->list_lock);
return result;
}
static bool aio_dispatch_handlers(AioContext *ctx)
{
AioHandler *node, *tmp;
bool progress = false;
/*
* We have to walk very carefully in case aio_set_fd_handler is
* called while we're walking.
*/
qemu_lockcnt_inc(&ctx->list_lock);
QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
int revents;
revents = node->pfd.revents & node->pfd.events;
node->pfd.revents = 0;
if (!node->deleted &&
(revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&
aio_node_check(ctx, node->is_external) &&
node->io_read) {
node->io_read(node->opaque);
/* aio_notify() does not count as progress */
if (node->opaque != &ctx->notifier) {
progress = true;
}
}
if (!node->deleted &&
(revents & (G_IO_OUT | G_IO_ERR)) &&
aio_node_check(ctx, node->is_external) &&
node->io_write) {
node->io_write(node->opaque);
progress = true;
}
if (node->deleted) {
if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {
QLIST_REMOVE(node, node);
g_free(node);
qemu_lockcnt_inc_and_unlock(&ctx->list_lock);
}
}
}
qemu_lockcnt_dec(&ctx->list_lock);
return progress;
}
/*
* Note that dispatch_fds == false has the side-effect of post-poning the
* freeing of deleted handlers.
*/
bool aio_dispatch(AioContext *ctx, bool dispatch_fds)
{
bool progress;
/*
* If there are callbacks left that have been queued, we need to call them.
* Do not call select in this case, because it is possible that the caller
* does not need a complete flush (as is the case for aio_poll loops).
*/
progress = aio_bh_poll(ctx);
if (dispatch_fds) {
progress |= aio_dispatch_handlers(ctx);
}
/* Run our timers */
progress |= timerlistgroup_run_timers(&ctx->tlg);
return progress;
}
/* These thread-local variables are used only in a small part of aio_poll
* around the call to the poll() system call. In particular they are not
* used while aio_poll is performing callbacks, which makes it much easier
* to think about reentrancy!
*
* Stack-allocated arrays would be perfect but they have size limitations;
* heap allocation is expensive enough that we want to reuse arrays across
* calls to aio_poll(). And because poll() has to be called without holding
* any lock, the arrays cannot be stored in AioContext. Thread-local data
* has none of the disadvantages of these three options.
*/
static __thread GPollFD *pollfds;
static __thread AioHandler **nodes;
static __thread unsigned npfd, nalloc;
static __thread Notifier pollfds_cleanup_notifier;
static void pollfds_cleanup(Notifier *n, void *unused)
{
g_assert(npfd == 0);
g_free(pollfds);
g_free(nodes);
nalloc = 0;
}
static void add_pollfd(AioHandler *node)
{
if (npfd == nalloc) {
if (nalloc == 0) {
pollfds_cleanup_notifier.notify = pollfds_cleanup;
qemu_thread_atexit_add(&pollfds_cleanup_notifier);
nalloc = 8;
} else {
g_assert(nalloc <= INT_MAX);
nalloc *= 2;
}
pollfds = g_renew(GPollFD, pollfds, nalloc);
nodes = g_renew(AioHandler *, nodes, nalloc);
}
nodes[npfd] = node;
pollfds[npfd] = (GPollFD) {
.fd = node->pfd.fd,
.events = node->pfd.events,
};
npfd++;
}
static bool run_poll_handlers_once(AioContext *ctx)
{
bool progress = false;
AioHandler *node;
QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
if (!node->deleted && node->io_poll &&
node->io_poll(node->opaque)) {
progress = true;
}
/* Caller handles freeing deleted nodes. Don't do it here. */
}
return progress;
}
/* run_poll_handlers:
* @ctx: the AioContext
* @max_ns: maximum time to poll for, in nanoseconds
*
* Polls for a given time.
*
* Note that ctx->notify_me must be non-zero so this function can detect
* aio_notify().
*
* Note that the caller must have incremented ctx->list_lock.
*
* Returns: true if progress was made, false otherwise
*/
static bool run_poll_handlers(AioContext *ctx, int64_t max_ns)
{
bool progress;
int64_t end_time;
assert(ctx->notify_me);
assert(qemu_lockcnt_count(&ctx->list_lock) > 0);
assert(ctx->poll_disable_cnt == 0);
trace_run_poll_handlers_begin(ctx, max_ns);
end_time = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + max_ns;
do {
progress = run_poll_handlers_once(ctx);
} while (!progress && qemu_clock_get_ns(QEMU_CLOCK_REALTIME) < end_time);
trace_run_poll_handlers_end(ctx, progress);
return progress;
}
/* try_poll_mode:
* @ctx: the AioContext
* @blocking: busy polling is only attempted when blocking is true
*
* ctx->notify_me must be non-zero so this function can detect aio_notify().
*
* Note that the caller must have incremented ctx->list_lock.
*
* Returns: true if progress was made, false otherwise
*/
static bool try_poll_mode(AioContext *ctx, bool blocking)
{
if (blocking && ctx->poll_max_ns && ctx->poll_disable_cnt == 0) {
/* See qemu_soonest_timeout() uint64_t hack */
int64_t max_ns = MIN((uint64_t)aio_compute_timeout(ctx),
(uint64_t)ctx->poll_ns);
if (max_ns) {
poll_set_started(ctx, true);
if (run_poll_handlers(ctx, max_ns)) {
return true;
}
}
}
poll_set_started(ctx, false);
/* Even if we don't run busy polling, try polling once in case it can make
* progress and the caller will be able to avoid ppoll(2)/epoll_wait(2).
*/
return run_poll_handlers_once(ctx);
}
bool aio_poll(AioContext *ctx, bool blocking)
{
AioHandler *node;
int i;
int ret = 0;
bool progress;
int64_t timeout;
int64_t start = 0;
aio_context_acquire(ctx);
progress = false;
/* aio_notify can avoid the expensive event_notifier_set if
* everything (file descriptors, bottom halves, timers) will
* be re-evaluated before the next blocking poll(). This is
* already true when aio_poll is called with blocking == false;
* if blocking == true, it is only true after poll() returns,
* so disable the optimization now.
*/
if (blocking) {
atomic_add(&ctx->notify_me, 2);
}
qemu_lockcnt_inc(&ctx->list_lock);
if (ctx->poll_max_ns) {
start = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
}
if (try_poll_mode(ctx, blocking)) {
progress = true;
} else {
assert(npfd == 0);
/* fill pollfds */
if (!aio_epoll_enabled(ctx)) {
QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
if (!node->deleted && node->pfd.events
&& aio_node_check(ctx, node->is_external)) {
add_pollfd(node);
}
}
}
timeout = blocking ? aio_compute_timeout(ctx) : 0;
/* wait until next event */
if (timeout) {
aio_context_release(ctx);
}
if (aio_epoll_check_poll(ctx, pollfds, npfd, timeout)) {
AioHandler epoll_handler;
epoll_handler.pfd.fd = ctx->epollfd;
epoll_handler.pfd.events = G_IO_IN | G_IO_OUT | G_IO_HUP | G_IO_ERR;
npfd = 0;
add_pollfd(&epoll_handler);
ret = aio_epoll(ctx, pollfds, npfd, timeout);
} else {
ret = qemu_poll_ns(pollfds, npfd, timeout);
}
if (timeout) {
aio_context_acquire(ctx);
}
}
if (blocking) {
atomic_sub(&ctx->notify_me, 2);
}
/* Adjust polling time */
if (ctx->poll_max_ns) {
int64_t block_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - start;
if (block_ns <= ctx->poll_ns) {
/* This is the sweet spot, no adjustment needed */
} else if (block_ns > ctx->poll_max_ns) {
/* We'd have to poll for too long, poll less */
int64_t old = ctx->poll_ns;
if (ctx->poll_shrink) {
ctx->poll_ns /= ctx->poll_shrink;
} else {
ctx->poll_ns = 0;
}
trace_poll_shrink(ctx, old, ctx->poll_ns);
} else if (ctx->poll_ns < ctx->poll_max_ns &&
block_ns < ctx->poll_max_ns) {
/* There is room to grow, poll longer */
int64_t old = ctx->poll_ns;
int64_t grow = ctx->poll_grow;
if (grow == 0) {
grow = 2;
}
if (ctx->poll_ns) {
ctx->poll_ns *= grow;
} else {
ctx->poll_ns = 4000; /* start polling at 4 microseconds */
}
if (ctx->poll_ns > ctx->poll_max_ns) {
ctx->poll_ns = ctx->poll_max_ns;
}
trace_poll_grow(ctx, old, ctx->poll_ns);
}
}
aio_notify_accept(ctx);
/* if we have any readable fds, dispatch event */
if (ret > 0) {
for (i = 0; i < npfd; i++) {
nodes[i]->pfd.revents = pollfds[i].revents;
}
}
npfd = 0;
qemu_lockcnt_dec(&ctx->list_lock);
/* Run dispatch even if there were no readable fds to run timers */
if (aio_dispatch(ctx, ret > 0)) {
progress = true;
}
aio_context_release(ctx);
return progress;
}
void aio_context_setup(AioContext *ctx)
{
/* TODO remove this in final patch submission */
if (getenv("QEMU_AIO_POLL_MAX_NS")) {
fprintf(stderr, "The QEMU_AIO_POLL_MAX_NS environment variable has "
"been replaced with -object iothread,poll-max-ns=NUM\n");
exit(1);
}
#ifdef CONFIG_EPOLL_CREATE1
assert(!ctx->epollfd);
ctx->epollfd = epoll_create1(EPOLL_CLOEXEC);
if (ctx->epollfd == -1) {
fprintf(stderr, "Failed to create epoll instance: %s", strerror(errno));
ctx->epoll_available = false;
} else {
ctx->epoll_available = true;
}
#endif
}
void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
int64_t grow, int64_t shrink, Error **errp)
{
/* No thread synchronization here, it doesn't matter if an incorrect value
* is used once.
*/
ctx->poll_max_ns = max_ns;
ctx->poll_ns = 0;
ctx->poll_grow = grow;
ctx->poll_shrink = shrink;
aio_notify(ctx);
}