From 84d61e5f36a73ed24742b7c7cf7b811e456dd024 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Wed, 13 Sep 2023 16:00:44 -0400 Subject: virtio: use defer_call() in virtio_irqfd_notify() virtio-blk and virtio-scsi invoke virtio_irqfd_notify() to send Used Buffer Notifications from an IOThread. This involves an eventfd write(2) syscall. Calling this repeatedly when completing multiple I/O requests in a row is wasteful. Use the defer_call() API to batch together virtio_irqfd_notify() calls made during thread pool (aio=threads), Linux AIO (aio=native), and io_uring (aio=io_uring) completion processing. Behavior is unchanged for emulated devices that do not use defer_call_begin()/defer_call_end() since defer_call() immediately invokes the callback when called outside a defer_call_begin()/defer_call_end() region. fio rw=randread bs=4k iodepth=64 numjobs=8 IOPS increases by ~9% with a single IOThread and 8 vCPUs. iodepth=1 decreases by ~1% but this could be noise. Detailed performance data and configuration specifics are available here: https://gitlab.com/stefanha/virt-playbooks/-/tree/blk_io_plug-irqfd This duplicates the BH that virtio-blk uses for batching. The next commit will remove it. Reviewed-by: Eric Blake Signed-off-by: Stefan Hajnoczi Message-ID: <20230913200045.1024233-4-stefanha@redhat.com> Reviewed-by: Michael S. Tsirkin Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- util/thread-pool.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'util/thread-pool.c') diff --git a/util/thread-pool.c b/util/thread-pool.c index 22f9ba3286..27eb777e85 100644 --- a/util/thread-pool.c +++ b/util/thread-pool.c @@ -15,6 +15,7 @@ * GNU GPL, version 2 or (at your option) any later version. */ #include "qemu/osdep.h" +#include "qemu/defer-call.h" #include "qemu/queue.h" #include "qemu/thread.h" #include "qemu/coroutine.h" @@ -175,6 +176,8 @@ static void thread_pool_completion_bh(void *opaque) ThreadPool *pool = opaque; ThreadPoolElement *elem, *next; + defer_call_begin(); /* cb() may use defer_call() to coalesce work */ + restart: QLIST_FOREACH_SAFE(elem, &pool->head, all, next) { if (elem->state != THREAD_DONE) { @@ -208,6 +211,8 @@ restart: qemu_aio_unref(elem); } } + + defer_call_end(); } static void thread_pool_cancel(BlockAIOCB *acb) -- cgit 1.4.1