diff options
| -rw-r--r-- | aio-posix.c | 78 | ||||
| -rw-r--r-- | async.c | 2 | ||||
| -rw-r--r-- | include/block/aio.h | 3 |
3 files changed, 57 insertions, 26 deletions
diff --git a/aio-posix.c b/aio-posix.c index cbd4c34..296cd9b 100644 --- a/aio-posix.c +++ b/aio-posix.c @@ -24,7 +24,6 @@ struct AioHandler IOHandler *io_read; IOHandler *io_write; int deleted; - int pollfds_idx; void *opaque; QLIST_ENTRY(AioHandler) node; }; @@ -83,7 +82,6 @@ void aio_set_fd_handler(AioContext *ctx, node->io_read = io_read; node->io_write = io_write; node->opaque = opaque; - node->pollfds_idx = -1; 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); @@ -186,12 +184,59 @@ bool aio_dispatch(AioContext *ctx) 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++; +} + bool aio_poll(AioContext *ctx, bool blocking) { AioHandler *node; bool was_dispatching; - int ret; + int i, ret; bool progress; + int64_t timeout; was_dispatching = ctx->dispatching; progress = false; @@ -210,39 +255,30 @@ bool aio_poll(AioContext *ctx, bool blocking) ctx->walking_handlers++; - g_array_set_size(ctx->pollfds, 0); + assert(npfd == 0); /* fill pollfds */ QLIST_FOREACH(node, &ctx->aio_handlers, node) { - node->pollfds_idx = -1; if (!node->deleted && node->pfd.events) { - GPollFD pfd = { - .fd = node->pfd.fd, - .events = node->pfd.events, - }; - node->pollfds_idx = ctx->pollfds->len; - g_array_append_val(ctx->pollfds, pfd); + add_pollfd(node); } } - ctx->walking_handlers--; + timeout = blocking ? aio_compute_timeout(ctx) : 0; /* wait until next event */ - ret = qemu_poll_ns((GPollFD *)ctx->pollfds->data, - ctx->pollfds->len, - blocking ? aio_compute_timeout(ctx) : 0); + ret = qemu_poll_ns((GPollFD *)pollfds, npfd, timeout); /* if we have any readable fds, dispatch event */ if (ret > 0) { - QLIST_FOREACH(node, &ctx->aio_handlers, node) { - if (node->pollfds_idx != -1) { - GPollFD *pfd = &g_array_index(ctx->pollfds, GPollFD, - node->pollfds_idx); - node->pfd.revents = pfd->revents; - } + for (i = 0; i < npfd; i++) { + nodes[i]->pfd.revents = pollfds[i].revents; } } + npfd = 0; + ctx->walking_handlers--; + /* Run dispatch even if there were no readable fds to run timers */ aio_set_dispatching(ctx, true); if (aio_dispatch(ctx)) { @@ -230,7 +230,6 @@ aio_ctx_finalize(GSource *source) event_notifier_cleanup(&ctx->notifier); rfifolock_destroy(&ctx->lock); qemu_mutex_destroy(&ctx->bh_lock); - g_array_free(ctx->pollfds, TRUE); timerlistgroup_deinit(&ctx->tlg); } @@ -302,7 +301,6 @@ AioContext *aio_context_new(Error **errp) aio_set_event_notifier(ctx, &ctx->notifier, (EventNotifierHandler *) event_notifier_test_and_clear); - ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD)); ctx->thread_pool = NULL; qemu_mutex_init(&ctx->bh_lock); rfifolock_init(&ctx->lock, aio_rfifolock_cb, ctx); diff --git a/include/block/aio.h b/include/block/aio.h index 7d1e26b..0dc7a25 100644 --- a/include/block/aio.h +++ b/include/block/aio.h @@ -82,9 +82,6 @@ struct AioContext { /* Used for aio_notify. */ EventNotifier notifier; - /* GPollFDs for aio_poll() */ - GArray *pollfds; - /* Thread pool for performing work and receiving completion callbacks */ struct ThreadPool *thread_pool; |