Module Name: src
Committed By: yamt
Date: Fri Apr 13 15:33:38 UTC 2012
Modified Files:
src/sys/uvm: uvm_emap.c
Log Message:
comments
To generate a diff of this commit:
cvs rdiff -u -r1.8 -r1.9 src/sys/uvm/uvm_emap.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/uvm/uvm_emap.c
diff -u src/sys/uvm/uvm_emap.c:1.8 src/sys/uvm/uvm_emap.c:1.9
--- src/sys/uvm/uvm_emap.c:1.8 Fri Sep 2 22:25:08 2011
+++ src/sys/uvm/uvm_emap.c Fri Apr 13 15:33:38 2012
@@ -1,4 +1,4 @@
-/* $NetBSD: uvm_emap.c,v 1.8 2011/09/02 22:25:08 dyoung Exp $ */
+/* $NetBSD: uvm_emap.c,v 1.9 2012/04/13 15:33:38 yamt Exp $ */
/*-
* Copyright (c) 2009, 2010 The NetBSD Foundation, Inc.
@@ -31,6 +31,40 @@
/*
* UVM ephemeral mapping interface.
+ */
+
+/*
+ * Overview:
+ *
+ * On multiprocessor systems, frequent uses of pmap_kenter_pa/pmap_kremove
+ * for ephemeral mappings are not desirable because they likely involve
+ * TLB flush IPIs because that pmap_kernel() is shared among all LWPs.
+ * This interface can be used instead, to reduce the number of IPIs.
+ *
+ * For a single-page mapping, PMAP_DIRECT_MAP is likely a better choice
+ * if available. (__HAVE_DIRECT_MAP)
+ */
+
+/*
+ * How to use:
+ *
+ * Map pages at the address:
+ *
+ * uvm_emap_enter(va, pgs, npages);
+ * gen = uvm_emap_produce();
+ *
+ * Read pages via the mapping:
+ *
+ * uvm_emap_consume(gen);
+ * some_access(va);
+ *
+ * After finishing using the mapping:
+ *
+ * uvm_emap_remove(va, len);
+ */
+
+/*
+ * Notes for pmap developers:
*
* Generic (more expensive) stubs are implemented for architectures which
* do not support pmap.
@@ -46,7 +80,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_emap.c,v 1.8 2011/09/02 22:25:08 dyoung Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_emap.c,v 1.9 2012/04/13 15:33:38 yamt Exp $");
#include <sys/param.h>
#include <sys/kernel.h>
