bool aio_poll(AioContext *ctx, bool blocking) { AioHandler *node; int i; int ret = 0; bool progress; int64_t timeout; int64_t start = 0; /* 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); } progress = try_poll_mode(ctx, blocking); if (!progress) { 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 (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 (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; } return progress; }