[src/trunk]: src/sys/sys - Give cwdi_lock its own cache line, for multithread...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/872e88a62268
branches:  trunk
changeset: 1009369:872e88a62268
user:      ad <ad%NetBSD.org@localhost>
date:      Tue Apr 21 21:46:07 2020 +0000

description:
- Give cwdi_lock its own cache line, for multithreaded processes.
- Comments.

diffstat:

 sys/sys/filedesc.h |  22 +++++++++++++++-------
 1 files changed, 15 insertions(+), 7 deletions(-)

diffs (37 lines):

diff -r f106f57ddb0c -r 872e88a62268 sys/sys/filedesc.h
--- a/sys/sys/filedesc.h        Tue Apr 21 21:42:47 2020 +0000
+++ b/sys/sys/filedesc.h        Tue Apr 21 21:46:07 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: filedesc.h,v 1.67 2020/04/21 21:42:47 ad Exp $ */
+/*     $NetBSD: filedesc.h,v 1.68 2020/04/21 21:46:07 ad Exp $ */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -164,13 +164,21 @@
        uint32_t        fd_dlomap[NDENTRIES];
 } filedesc_t;
 
+/*
+ * Working directory, root and umask information.  Serialization:
+ *
+ * a   atomic operations
+ * l   cwdi_lock
+ */
 typedef struct cwdinfo {
-       struct vnode    *cwdi_cdir;     /* current directory */
-       struct vnode    *cwdi_rdir;     /* root directory */
-       struct vnode    *cwdi_edir;     /* emulation root (if known) */
-       krwlock_t       cwdi_lock;      /* lock on entire struct */
-       u_int           cwdi_cmask;     /* mask for file creation */
-       u_int           cwdi_refcnt;    /* reference count */
+       struct vnode    *cwdi_cdir;     /* l: current directory */
+       struct vnode    *cwdi_rdir;     /* l: root directory */
+       struct vnode    *cwdi_edir;     /* l: emulation root (if known) */
+       u_int           cwdi_cmask;     /* a: mask for file creation */
+       u_int           cwdi_refcnt;    /* a: reference count */
+
+       krwlock_t       cwdi_lock       /* :: lock on struct */
+           __aligned(COHERENCY_UNIT);  /* -> gets own cache line */
 } cwdinfo_t;
 
 #ifdef _KERNEL