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authorImran Khan <imran.f.khan@oracle.com>2023-03-09 22:09:30 +1100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2023-03-29 12:23:45 +0200
commit9caf696142252a466fb89e629d0eddcdced027b0 (patch)
tree5b113ad7c36cd7129b34c3409c24b89d0ba45864
parent02fe26f25325b547b7a31a65deb0326c04bb5174 (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>
-rw-r--r--fs/kernfs/dir.c7
-rw-r--r--fs/kernfs/inode.c16
-rw-r--r--fs/kernfs/kernfs-internal.h1
3 files changed, 16 insertions, 8 deletions
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index ef00b5fe8cee..953b2717c60e 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -770,12 +770,15 @@ int kernfs_add_one(struct kernfs_node *kn)
goto out_unlock;
/* Update timestamps on the parent */
+ down_write(&root->kernfs_iattr_rwsem);
+
ps_iattr = parent->iattr;
if (ps_iattr) {
ktime_get_real_ts64(&ps_iattr->ia_ctime);
ps_iattr->ia_mtime = ps_iattr->ia_ctime;
}
+ up_write(&root->kernfs_iattr_rwsem);
up_write(&root->kernfs_rwsem);
/*
@@ -940,6 +943,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
idr_init(&root->ino_idr);
init_rwsem(&root->kernfs_rwsem);
+ init_rwsem(&root->kernfs_iattr_rwsem);
INIT_LIST_HEAD(&root->supers);
/*
@@ -1462,11 +1466,14 @@ static void __kernfs_remove(struct kernfs_node *kn)
pos->parent ? pos->parent->iattr : NULL;
/* update timestamps on the parent */
+ down_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
+
if (ps_iattr) {
ktime_get_real_ts64(&ps_iattr->ia_ctime);
ps_iattr->ia_mtime = ps_iattr->ia_ctime;
}
+ up_write(&kernfs_root(kn)->kernfs_iattr_rwsem);
kernfs_put(pos);
}
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;
}
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 236c3a6113f1..3297093c920d 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -47,6 +47,7 @@ struct kernfs_root {
wait_queue_head_t deactivate_waitq;
struct rw_semaphore kernfs_rwsem;
+ struct rw_semaphore kernfs_iattr_rwsem;
};
/* +1 to avoid triggering overflow warning when negating it */