Module Name: src
Committed By: riastradh
Date: Wed Aug 2 07:11:31 UTC 2023
Modified Files:
src/sys/kern: kern_fileassoc.c
Log Message:
fileassoc(9): Fast paths to skip global locks when not in use.
PR kern/57552
To generate a diff of this commit:
cvs rdiff -u -r1.36 -r1.37 src/sys/kern/kern_fileassoc.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_fileassoc.c
diff -u src/sys/kern/kern_fileassoc.c:1.36 src/sys/kern/kern_fileassoc.c:1.37
--- src/sys/kern/kern_fileassoc.c:1.36 Thu Jul 10 15:00:28 2014
+++ src/sys/kern/kern_fileassoc.c Wed Aug 2 07:11:31 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_fileassoc.c,v 1.36 2014/07/10 15:00:28 christos Exp $ */
+/* $NetBSD: kern_fileassoc.c,v 1.37 2023/08/02 07:11:31 riastradh Exp $ */
/*-
* Copyright (c) 2006 Elad Efrat <[email protected]>
@@ -28,7 +28,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_fileassoc.c,v 1.36 2014/07/10 15:00:28 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_fileassoc.c,v 1.37 2023/08/02 07:11:31 riastradh Exp $");
#include "opt_fileassoc.h"
@@ -42,6 +42,8 @@ __KERNEL_RCSID(0, "$NetBSD: kern_fileass
#include <sys/hash.h>
#include <sys/kmem.h>
#include <sys/once.h>
+#include <sys/mutex.h>
+#include <sys/xcall.h>
#define FILEASSOC_INITIAL_TABLESIZE 128
@@ -88,6 +90,52 @@ struct fileassoc_table {
(hash32_buf((handle), FHANDLE_SIZE(handle), HASH32_BUF_INIT) \
& ((tbl)->tbl_mask))
+/*
+ * Global usage counting. This is bad for parallelism of updates, but
+ * good for avoiding calls to fileassoc when it's not in use. Unclear
+ * if parallelism of updates matters much. If you want to improve
+ * fileassoc(9) update performance, feel free to rip this out as long
+ * as you don't cause the fast paths to take any global locks or incur
+ * memory barriers when fileassoc(9) is not in use.
+ */
+static struct {
+ kmutex_t lock;
+ uint64_t nassocs;
+ volatile bool inuse;
+} fileassoc_global __cacheline_aligned;
+
+static void
+fileassoc_incuse(void)
+{
+
+ mutex_enter(&fileassoc_global.lock);
+ if (fileassoc_global.nassocs++ == 0) {
+ KASSERT(!fileassoc_global.inuse);
+ atomic_store_relaxed(&fileassoc_global.inuse, true);
+ xc_barrier(0);
+ }
+ mutex_exit(&fileassoc_global.lock);
+}
+
+static void
+fileassoc_decuse(void)
+{
+
+ mutex_enter(&fileassoc_global.lock);
+ KASSERT(fileassoc_global.nassocs > 0);
+ KASSERT(fileassoc_global.inuse);
+ if (--fileassoc_global.nassocs == 0)
+ atomic_store_relaxed(&fileassoc_global.inuse, false);
+ mutex_exit(&fileassoc_global.lock);
+}
+
+static bool
+fileassoc_inuse(void)
+{
+
+ return __predict_false(atomic_load_relaxed(&fileassoc_global.inuse));
+}
+
static void *
file_getdata(struct fileassoc_file *faf, const struct fileassoc *assoc)
{
@@ -128,6 +176,7 @@ file_free(struct fileassoc_file *faf)
LIST_FOREACH(assoc, &fileassoc_list, assoc_list) {
file_cleanup(faf, assoc);
+ fileassoc_decuse();
}
vfs_composefh_free(faf->faf_handle);
specificdata_fini(fileassoc_domain, &faf->faf_data);
@@ -226,6 +275,9 @@ fileassoc_table_lookup(struct mount *mp)
{
int error;
+ if (!fileassoc_inuse())
+ return NULL;
+
error = RUN_ONCE(&control, fileassoc_init);
if (error) {
return NULL;
@@ -437,6 +489,8 @@ fileassoc_table_clear(struct mount *mp,
LIST_FOREACH(faf, &tbl->tbl_hash[i], faf_list) {
file_cleanup(faf, assoc);
file_setdata(faf, assoc, NULL);
+ /* XXX missing faf->faf_nassocs--? */
+ fileassoc_decuse();
}
}
@@ -510,10 +564,9 @@ fileassoc_file_delete(struct vnode *vp)
struct fileassoc_table *tbl;
struct fileassoc_file *faf;
- /* Pre-check if fileassoc is used. XXX */
- if (!fileassoc_domain) {
+ if (!fileassoc_inuse())
return ENOENT;
- }
+
KERNEL_LOCK(1, NULL);
faf = fileassoc_file_lookup(vp, NULL);
@@ -553,6 +606,8 @@ fileassoc_add(struct vnode *vp, fileasso
if (olddata != NULL)
return (EEXIST);
+ fileassoc_incuse();
+
file_setdata(faf, assoc, data);
faf->faf_nassocs++;
@@ -577,5 +632,7 @@ fileassoc_clear(struct vnode *vp, fileas
--(faf->faf_nassocs); /* XXX gc? */
+ fileassoc_decuse();
+
return (0);
}
