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Use io_uring_register_ring_fd() to skip fd operations

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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@gmail.com>
Message-id: 20220531105011.111082-1-faithilikerun@gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Sam Li 2022-05-31 18:50:11 +08:00 committed by Stefan Hajnoczi
parent 9e4067b8a4
commit e2848bc574
2 changed files with 12 additions and 1 deletions
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12
block/io_uring.c
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@ -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)

1
meson.build
View file

@ -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())