On Thu, 2015-10-29 at 05:35 -0700, Eric Dumazet wrote:
> Current kernel :
>
> 64.98% [kernel] [k] queued_spin_lock_slowpath
> 14.88% opensock [.] memset // this part simulates user land actual work ;)
> 11.15% [kernel] [k] _find_next_bit.part.0
> 0.69% [kernel] [k] _raw_spin_lock
> 0.46% [kernel] [k] memset_erms
> 0.38% [kernel] [k] sk_alloc
> 0.37% [kernel] [k] kmem_cache_alloc
> 0.33% [kernel] [k] get_empty_filp
> 0.31% [kernel] [k] kmem_cache_free
> 0.26% [kernel] [k] __alloc_fd
> 0.26% opensock [.] child_function
> 0.18% [kernel] [k] inode_init_always
> 0.17% opensock [.] __random_r
With attached prototype patch we get this profile instead :
You can see we no longer hit the spinlock issue and cache waste
in find_next_bit.
Userland can really progress _much_ faster.
76.86% opensock [.] memset
1.31% [kernel] [k] _raw_spin_lock
1.15% assd [.] 0x000000000056f32c
1.08% [kernel] [k] kmem_cache_free
0.97% [kernel] [k] kmem_cache_alloc
0.83% [kernel] [k] sk_alloc
0.72% [kernel] [k] memset_erms
0.70% opensock [.] child_function
0.67% [kernel] [k] get_empty_filp
0.65% [kernel] [k] __alloc_fd
0.58% [kernel] [k] __close_fd
0.49% [kernel] [k] queued_spin_lock_slowpath
diff --git a/fs/file.c b/fs/file.c
index 6c672ad329e9..eabb9a626259 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -22,6 +22,7 @@
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
+#include <linux/random.h>
int sysctl_nr_open __read_mostly = 1024*1024;
int sysctl_nr_open_min = BITS_PER_LONG;
@@ -471,6 +472,19 @@ int __alloc_fd(struct files_struct *files,
spin_lock(&files->file_lock);
repeat:
fdt = files_fdtable(files);
+
+ if (unlikely(flags & O_FD_FASTALLOC)) {
+ u32 rnd, limit = min(end, fdt->max_fds);
+
+ /*
+ * Note: do not bother with files->next_fd,
+ * this is for POSIX lovers...
+ */
+ rnd = ((u64)prandom_u32() * limit) >> 32;
+ fd = find_next_zero_bit(fdt->open_fds, limit, rnd);
+ if (fd < limit)
+ goto ok;
+ }
fd = start;
if (fd < files->next_fd)
fd = files->next_fd;
@@ -499,7 +513,7 @@ repeat:
if (start <= files->next_fd)
files->next_fd = fd + 1;
-
+ok:
__set_open_fd(fd, fdt);
if (flags & O_CLOEXEC)
__set_close_on_exec(fd, fdt);
diff --git a/include/linux/net.h b/include/linux/net.h
index 70ac5e28e6b7..3823d082af4c 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -76,6 +76,7 @@ enum sock_type {
#ifndef SOCK_NONBLOCK
#define SOCK_NONBLOCK O_NONBLOCK
#endif
+#define SOCK_FD_FASTALLOC O_FD_FASTALLOC
#endif /* ARCH_HAS_SOCKET_TYPES */
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index e063effe0cc1..badd421dd9f4 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -88,6 +88,10 @@
#define __O_TMPFILE 020000000
#endif
+#ifndef O_FD_FASTALLOC
+#define O_FD_FASTALLOC 0x40000000
+#endif
+
/* a horrid kludge trying to make sure that this will fail on old kernels */
#define O_TMPFILE (__O_TMPFILE | O_DIRECTORY)
#define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT)
diff --git a/net/socket.c b/net/socket.c
index 9963a0b53a64..6dde02b2eaf9 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1227,9 +1227,10 @@ SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
BUILD_BUG_ON((SOCK_MAX | SOCK_TYPE_MASK) != SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_CLOEXEC & SOCK_TYPE_MASK);
BUILD_BUG_ON(SOCK_NONBLOCK & SOCK_TYPE_MASK);
+ BUILD_BUG_ON(SOCK_FD_FASTALLOC & SOCK_TYPE_MASK);
flags = type & ~SOCK_TYPE_MASK;
- if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
+ if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK | SOCK_FD_FASTALLOC))
return -EINVAL;
type &= SOCK_TYPE_MASK;
@@ -1240,7 +1241,7 @@ SYSCALL_DEFINE3(socket, int, family, int, type, int, protocol)
if (retval < 0)
goto out;
- retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK));
+ retval = sock_map_fd(sock, flags & (O_CLOEXEC | O_NONBLOCK | O_FD_FASTALLOC));
if (retval < 0)
goto out_release;
@@ -1266,7 +1267,7 @@ SYSCALL_DEFINE4(socketpair, int, family, int, type, int, protocol,
int flags;
flags = type & ~SOCK_TYPE_MASK;
- if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
+ if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK | SOCK_FD_FASTALLOC))
return -EINVAL;
type &= SOCK_TYPE_MASK;
@@ -1436,7 +1437,7 @@ SYSCALL_DEFINE4(accept4, int, fd, struct sockaddr __user *, upeer_sockaddr,
int err, len, newfd, fput_needed;
struct sockaddr_storage address;
- if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK))
+ if (flags & ~(SOCK_CLOEXEC | SOCK_NONBLOCK | SOCK_FD_FASTALLOC))
return -EINVAL;
if (SOCK_NONBLOCK != O_NONBLOCK && (flags & SOCK_NONBLOCK))
--
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