From e2848bc574fe2715c694bf8fe9a1ba7f78a1125a Mon Sep 17 00:00:00 2001 From: Sam Li Date: Tue, 31 May 2022 18:50:11 +0800 Subject: [PATCH] Use io_uring_register_ring_fd() to skip fd operations Linux recently added a new io_uring(7) optimization API that QEMU doesn't take advantage of yet. The liburing library that QEMU uses has added a corresponding new API calling io_uring_register_ring_fd(). When this API is called after creating the ring, the io_uring_submit() library function passes a flag to the io_uring_enter(2) syscall allowing it to skip the ring file descriptor fdget()/fdput() operations. This saves some CPU cycles. Signed-off-by: Sam Li Message-id: 20220531105011.111082-1-faithilikerun@gmail.com Signed-off-by: Stefan Hajnoczi --- block/io_uring.c | 12 +++++++++++- meson.build | 1 + 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/block/io_uring.c b/block/io_uring.c index 0b401512b9..d48e472e74 100644 --- a/block/io_uring.c +++ b/block/io_uring.c @@ -18,6 +18,7 @@ #include "qapi/error.h" #include "trace.h" + /* io_uring ring size */ #define MAX_ENTRIES 128 @@ -434,8 +435,17 @@ LuringState *luring_init(Error **errp) } ioq_init(&s->io_q); - return s; +#ifdef CONFIG_LIBURING_REGISTER_RING_FD + if (io_uring_register_ring_fd(&s->ring) < 0) { + /* + * Only warn about this error: we will fallback to the non-optimized + * io_uring operations. + */ + warn_report("failed to register linux io_uring ring file descriptor"); + } +#endif + return s; } void luring_cleanup(LuringState *s) diff --git a/meson.build b/meson.build index 0c2e11ff07..9e65cc5367 100644 --- a/meson.build +++ b/meson.build @@ -1752,6 +1752,7 @@ config_host_data.set('CONFIG_LIBNFS', libnfs.found()) config_host_data.set('CONFIG_LIBSSH', libssh.found()) config_host_data.set('CONFIG_LINUX_AIO', libaio.found()) config_host_data.set('CONFIG_LINUX_IO_URING', linux_io_uring.found()) +config_host_data.set('CONFIG_LIBURING_REGISTER_RING_FD', cc.has_function('io_uring_register_ring_fd', prefix: '#include ', dependencies:linux_io_uring)) config_host_data.set('CONFIG_LIBPMEM', libpmem.found()) config_host_data.set('CONFIG_NUMA', numa.found()) config_host_data.set('CONFIG_OPENGL', opengl.found())