Drop CACHE_LINE_SIZE to 64 bytes on x86

The actual cache line size has always been 64 bytes.

The 128 number arose as an optimization for Core 2 era Intel processors.  By
default (configurable in BIOS), these CPUs would prefetch adjacent cache
lines unintelligently.  Newer CPUs prefetch more intelligently.

The latest Core 2 era CPU was introduced in September 2008 (Xeon 7400
series, "Dunnington").  If you are still using one of these CPUs, especially
in a multi-socket configuration, consider locating the "adjacent cache line
prefetch" option in BIOS and disabling it.

Reported by:	mjg
Reviewed by:	np
Discussed with:	jhb
Sponsored by:	Dell EMC Isilon
This commit is contained in:
Conrad Meyer 2017-08-28 22:28:41 +00:00
parent 0cc18edf18
commit 2744a0b69b
3 changed files with 3 additions and 3 deletions
sys
amd64/include
i386/include
sys

@ -89,7 +89,7 @@
* CACHE_LINE_SIZE is the compile-time maximum cache line size for an
* architecture. It should be used with appropriate caution.
*/
#define CACHE_LINE_SHIFT 7
#define CACHE_LINE_SHIFT 6
#define CACHE_LINE_SIZE (1 << CACHE_LINE_SHIFT)
/* Size of the level 1 page table units */

@ -82,7 +82,7 @@
* CACHE_LINE_SIZE is the compile-time maximum cache line size for an
* architecture. It should be used with appropriate caution.
*/
#define CACHE_LINE_SHIFT 7
#define CACHE_LINE_SHIFT 6
#define CACHE_LINE_SIZE (1 << CACHE_LINE_SHIFT)
#define PAGE_SHIFT 12 /* LOG2(PAGE_SIZE) */

@ -58,7 +58,7 @@
* in the range 5 to 9.
*/
#undef __FreeBSD_version
#define __FreeBSD_version 1200042 /* Master, propagated to newvers */
#define __FreeBSD_version 1200043 /* Master, propagated to newvers */
/*
* __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,