[Virtio-fs] [PULL 02/18] Use io_uring_register_ring_fd() to skip fd operations
Stefan Hajnoczi
stefanha at redhat.com
Wed Jun 15 15:51:13 UTC 2022
From: Sam Li <faithilikerun at gmail.com>
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 <faithilikerun at gmail.com>
Message-id: 20220531105011.111082-1-faithilikerun at gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha at redhat.com>
---
meson.build | 1 +
block/io_uring.c | 12 +++++++++++-
2 files changed, 12 insertions(+), 1 deletion(-)
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 <liburing.h>', 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())
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);
+#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)
--
2.36.1
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