linux/arch/tile/include/asm/cache.h
Chris Metcalf ce61cdc270 tile: make __write_once a synonym for __read_mostly
This was really only useful for TILE64 when we mapped the
kernel data with small pages. Now we use a huge page and we
really don't want to map different parts of the kernel
data in different ways.

We retain the __write_once name in case we want to bring
it back to life at some point in the future.

Note that this change uncovered a latent bug where the
"smp_topology" variable happened to always be aligned mod 8
so we could store two "int" values at once, but when we
eliminated __write_once it ended up only aligned mod 4.
Fix with an explicit annotation.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
2013-09-03 14:53:32 -04:00

65 lines
2.6 KiB
C

/*
* Copyright 2010 Tilera Corporation. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*/
#ifndef _ASM_TILE_CACHE_H
#define _ASM_TILE_CACHE_H
#include <arch/chip.h>
/* bytes per L1 data cache line */
#define L1_CACHE_SHIFT CHIP_L1D_LOG_LINE_SIZE()
#define L1_CACHE_BYTES (1 << L1_CACHE_SHIFT)
/* bytes per L2 cache line */
#define L2_CACHE_SHIFT CHIP_L2_LOG_LINE_SIZE()
#define L2_CACHE_BYTES (1 << L2_CACHE_SHIFT)
#define L2_CACHE_ALIGN(x) (((x)+(L2_CACHE_BYTES-1)) & -L2_CACHE_BYTES)
/*
* TILEPro I/O is not always coherent (networking typically uses coherent
* I/O, but PCI traffic does not) and setting ARCH_DMA_MINALIGN to the
* L2 cacheline size helps ensure that kernel heap allocations are aligned.
* TILE-Gx I/O is always coherent when used on hash-for-home pages.
*
* However, it's possible at runtime to request not to use hash-for-home
* for the kernel heap, in which case the kernel will use flush-and-inval
* to manage coherence. As a result, we use L2_CACHE_BYTES for the
* DMA minimum alignment to avoid false sharing in the kernel heap.
*/
#define ARCH_DMA_MINALIGN L2_CACHE_BYTES
/* use the cache line size for the L2, which is where it counts */
#define SMP_CACHE_BYTES_SHIFT L2_CACHE_SHIFT
#define SMP_CACHE_BYTES L2_CACHE_BYTES
#define INTERNODE_CACHE_SHIFT L2_CACHE_SHIFT
#define INTERNODE_CACHE_BYTES L2_CACHE_BYTES
/* Group together read-mostly things to avoid cache false sharing */
#define __read_mostly __attribute__((__section__(".data..read_mostly")))
/*
* Originally we used small TLB pages for kernel data and grouped some
* things together as "write once", enforcing the property at the end
* of initialization by making those pages read-only and non-coherent.
* This allowed better cache utilization since cache inclusion did not
* need to be maintained. However, to do this requires an extra TLB
* entry, which on balance is more of a performance hit than the
* non-coherence is a performance gain, so we now just make "read
* mostly" and "write once" be synonyms. We keep the attribute
* separate in case we change our minds at a future date.
*/
#define __write_once __read_mostly
#endif /* _ASM_TILE_CACHE_H */