diff options
author | Imran Khan <imran.f.khan@oracle.com> | 2023-03-09 22:09:30 +1100 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-03-29 12:23:45 +0200 |
commit | 9caf696142252a466fb89e629d0eddcdced027b0 (patch) | |
tree | 5b113ad7c36cd7129b34c3409c24b89d0ba45864 /fs/kernfs/inode.c | |
parent | 02fe26f25325b547b7a31a65deb0326c04bb5174 (diff) |
kernfs: Introduce separate rwsem to protect inode attributes.
Right now a global per-fs rwsem (kernfs_rwsem) synchronizes multiple
kernfs operations. On a large system with few hundred CPUs and few
hundred applications simultaneoulsy trying to access sysfs, this
results in multiple sys_open(s) contending on kernfs_rwsem via
kernfs_iop_permission and kernfs_dop_revalidate.
For example on a system with 384 cores, if I run 200 instances of an
application which is mostly executing the following loop:
for (int loop = 0; loop <100 ; loop++)
{
for (int port_num = 1; port_num < 2; port_num++)
{
for (int gid_index = 0; gid_index < 254; gid_index++ )
{
char ret_buf[64], ret_buf_lo[64];
char gid_file_path[1024];
int ret_len;
int ret_fd;
ssize_t ret_rd;
ub4 i, saved_errno;
memset(ret_buf, 0, sizeof(ret_buf));
memset(gid_file_path, 0, sizeof(gid_file_path));
ret_len = snprintf(gid_file_path, sizeof(gid_file_path),
"/sys/class/infiniband/%s/ports/%d/gids/%d",
dev_name,
port_num,
gid_index);
ret_fd = open(gid_file_path, O_RDONLY | O_CLOEXEC);
if (ret_fd < 0)
{
printf("Failed to open %s\n", gid_file_path);
continue;
}
/* Read the GID */
ret_rd = read(ret_fd, ret_buf, 40);
if (ret_rd == -1)
{
printf("Failed to read from file %s, errno: %u\n",
gid_file_path, saved_errno);
continue;
}
close(ret_fd);
}
}
I see contention around kernfs_rwsem as follows:
path_openat
|
|----link_path_walk.part.0.constprop.0
| |
| |--49.92%--inode_permission
| | |
| | --48.69%--kernfs_iop_permission
| | |
| | |--18.16%--down_read
| | |
| | |--15.38%--up_read
| | |
| | --14.58%--_raw_spin_lock
| | |
| | -----
| |
| |--29.08%--walk_component
| | |
| | --29.02%--lookup_fast
| | |
| | |--24.26%--kernfs_dop_revalidate
| | | |
| | | |--14.97%--down_read
| | | |
| | | --9.01%--up_read
| | |
| | --4.74%--__d_lookup
| | |
| | --4.64%--_raw_spin_lock
| | |
| | ----
Having a separate per-fs rwsem to protect kernfs inode attributes,
will avoid the above mentioned contention and result in better
performance as can bee seen below:
path_openat
|
|----link_path_walk.part.0.constprop.0
| |
| |
| |--27.06%--inode_permission
| | |
| | --25.84%--kernfs_iop_permission
| | |
| | |--9.29%--up_read
| | |
| | |--8.19%--down_read
| | |
| | --7.89%--_raw_spin_lock
| | |
| | ----
| |
| |--22.42%--walk_component
| | |
| | --22.36%--lookup_fast
| | |
| | |--16.07%--__d_lookup
| | | |
| | | --16.01%--_raw_spin_lock
| | | |
| | | ----
| | |
| | --6.28%--kernfs_dop_revalidate
| | |
| | |--3.76%--down_read
| | |
| | --2.26%--up_read
As can be seen from the above data the overhead due to both
kerfs_iop_permission and kernfs_dop_revalidate have gone down and
this also reduces overall run time of the earlier mentioned loop.
Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Link: https://lore.kernel.org/r/20230309110932.2889010-2-imran.f.khan@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs/kernfs/inode.c')
-rw-r--r-- | fs/kernfs/inode.c | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c index 30494dcb0df3..b22b74d1a115 100644 --- a/fs/kernfs/inode.c +++ b/fs/kernfs/inode.c @@ -101,9 +101,9 @@ int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr) int ret; struct kernfs_root *root = kernfs_root(kn); - down_write(&root->kernfs_rwsem); + down_write(&root->kernfs_iattr_rwsem); ret = __kernfs_setattr(kn, iattr); - up_write(&root->kernfs_rwsem); + up_write(&root->kernfs_iattr_rwsem); return ret; } @@ -119,7 +119,7 @@ int kernfs_iop_setattr(struct mnt_idmap *idmap, struct dentry *dentry, return -EINVAL; root = kernfs_root(kn); - down_write(&root->kernfs_rwsem); + down_write(&root->kernfs_iattr_rwsem); error = setattr_prepare(&nop_mnt_idmap, dentry, iattr); if (error) goto out; @@ -132,7 +132,7 @@ int kernfs_iop_setattr(struct mnt_idmap *idmap, struct dentry *dentry, setattr_copy(&nop_mnt_idmap, inode, iattr); out: - up_write(&root->kernfs_rwsem); + up_write(&root->kernfs_iattr_rwsem); return error; } @@ -189,10 +189,10 @@ int kernfs_iop_getattr(struct mnt_idmap *idmap, struct kernfs_node *kn = inode->i_private; struct kernfs_root *root = kernfs_root(kn); - down_read(&root->kernfs_rwsem); + down_read(&root->kernfs_iattr_rwsem); kernfs_refresh_inode(kn, inode); generic_fillattr(&nop_mnt_idmap, inode, stat); - up_read(&root->kernfs_rwsem); + up_read(&root->kernfs_iattr_rwsem); return 0; } @@ -285,10 +285,10 @@ int kernfs_iop_permission(struct mnt_idmap *idmap, kn = inode->i_private; root = kernfs_root(kn); - down_read(&root->kernfs_rwsem); + down_read(&root->kernfs_iattr_rwsem); kernfs_refresh_inode(kn, inode); ret = generic_permission(&nop_mnt_idmap, inode, mask); - up_read(&root->kernfs_rwsem); + up_read(&root->kernfs_iattr_rwsem); return ret; } |