Alan Cox wrote:
John Baldwin wrote:
Alan Cox wrote:
Author: alc
Date: Sun Oct 4 18:53:10 2009
New Revision: 197750
URL: http://svn.freebsd.org/changeset/base/197750
Log:
Align and pad the page queue and free page queue locks so that the
linker
can't possibly place them together within the same cache line.
MFC after: 3 weeks
Modified:
head/sys/vm/vm_page.c
head/sys/vm/vm_page.h
Modified: head/sys/vm/vm_page.c
==============================================================================
--- head/sys/vm/vm_page.c Sun Oct 4 17:22:51 2009 (r197749)
+++ head/sys/vm/vm_page.c Sun Oct 4 18:53:10 2009 (r197750)
@@ -135,8 +135,8 @@ __FBSDID("$FreeBSD$");
*/
struct vpgqueues vm_page_queues[PQ_COUNT];
-struct mtx vm_page_queue_mtx;
-struct mtx vm_page_queue_free_mtx;
+struct vpglocks vm_page_queue_lock;
+struct vpglocks vm_page_queue_free_lock;
I think you can do this by just:
struct mtx vm_page_queue_mtx __aligned(CACHE_LINE_SIZE);
without the need for a wrapper structure.
Unfortunately, no. When I compile the following example:
int a;
int b __attribute__((aligned(16)));
int x;
int y;
int z;
int
main(void)
{
return (0);
}
I get the following:
080495b4 A __bss_start
080495b4 A _edata
080495c0 b completed.4860
080495c4 B environ
080495d0 B b
080495d4 B x
080495d8 B z
080495dc B y
080495e0 B a
080495e4 A _end
Thus, "b" is aligned as specified, but not padded to 16 bytes.
Do you care what is in the padding in this case or more about just
having each mutex on a separate cache line? __aligned() is fine if you
don't mind the padding getting reused for something else.
--
John Baldwin
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