Commit ce61cdc2 authored by Chris Metcalf's avatar Chris Metcalf
Browse files

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: default avatarChris Metcalf <cmetcalf@tilera.com>
parent d7c96611

arch/tile/include/asm/cache.h

+10 −3
Original line number Diff line number Diff line
@@ -49,9 +49,16 @@ 
#define __read_mostly __attribute__((__section__(".data..read_mostly")))



/*

 * Attribute for data that is kept read/write coherent until the end of

 * initialization, then bumped to read/only incoherent for performance.

 * 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 __attribute__((__section__(".w1data")))

#define __write_once __read_mostly



#endif /* _ASM_TILE_CACHE_H */

arch/tile/kernel/smp.c

+5 −1
Original line number Diff line number Diff line
@@ -22,7 +22,11 @@ 
#include <asm/cacheflush.h>

#include <asm/homecache.h>



HV_Topology smp_topology __write_once;

/*

 * We write to width and height with a single store in head_NN.S,

 * so make the variable aligned to "long".

 */

HV_Topology smp_topology __write_once __aligned(sizeof(long));

EXPORT_SYMBOL(smp_topology);



#if CHIP_HAS_IPI()

arch/tile/kernel/vmlinux.lds.S

+0 −12
Original line number Diff line number Diff line
@@ -74,20 +74,8 @@ SECTIONS 
  __init_end = .;



  _sdata = .;                   /* Start of data section */



  RO_DATA_SECTION(PAGE_SIZE)



  /* initially writeable, then read-only */

  . = ALIGN(PAGE_SIZE);

  __w1data_begin = .;

  .w1data : AT(ADDR(.w1data) - LOAD_OFFSET) {

    VMLINUX_SYMBOL(__w1data_begin) = .;

    *(.w1data)

    VMLINUX_SYMBOL(__w1data_end) = .;

  }



  RW_DATA_SECTION(L2_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)



  _edata = .;



  EXCEPTION_TABLE(L2_CACHE_BYTES)

arch/tile/mm/init.c

+2 −11
Original line number Diff line number Diff line
@@ -270,14 +270,6 @@ static pgprot_t __init init_pgprot(ulong address) 
	if (kdata_hash)

		return construct_pgprot(PAGE_KERNEL, PAGE_HOME_HASH);



	/*

	 * Make the w1data homed like heap to start with, to avoid

	 * making it part of the page-striped data area when we're just

	 * going to convert it to read-only soon anyway.

	 */

	if (address >= (ulong)__w1data_begin && address < (ulong)__w1data_end)

		return construct_pgprot(PAGE_KERNEL, initial_heap_home());



	/*

	 * Otherwise we just hand out consecutive cpus.  To avoid

	 * requiring this function to hold state, we just walk forward from
@@ -285,7 +277,7 @@ static pgprot_t __init init_pgprot(ulong address) 
	 * the requested address, while walking cpu home around kdata_mask.

	 * This is typically no more than a dozen or so iterations.

	 */

	page = (((ulong)__w1data_end) + PAGE_SIZE - 1) & PAGE_MASK;

	page = (((ulong)__end_rodata) + PAGE_SIZE - 1) & PAGE_MASK;

	BUG_ON(address < page || address >= (ulong)_end);

	cpu = cpumask_first(&kdata_mask);

	for (; page < address; page += PAGE_SIZE) {
@@ -980,8 +972,7 @@ void free_initmem(void) 
	const unsigned long text_delta = MEM_SV_START - PAGE_OFFSET;



	/*

	 * Evict the dirty initdata on the boot cpu, evict the w1data

	 * wherever it's homed, and evict all the init code everywhere.

	 * Evict the cache on all cores to avoid incoherence.

	 * We are guaranteed that no one will touch the init pages any more.

	 */

	homecache_evict(&cpu_cacheable_map);

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