powerpc/64s: Reduce exception alignment

Exception handlers are aligned to 128 bytes (L1 cache) on 64s, which is
overkill. It can reduce the icache footprint of any individual exception
path. However taken as a whole, the expansion in icache footprint seems
likely to be counter-productive and cause more total misses.

Create IFETCH_ALIGN_SHIFT/BYTES, which should give optimal ifetch
alignment with much more reasonable alignment. This saves 1792 bytes
from head_64.o text with an allmodconfig build.

Other subarchitectures should define appropriate IFETCH_ALIGN_SHIFT
values if this becomes more widely used.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/cache.h b/arch/powerpc/include/asm/cache.h
index ffbafbf76b193a28338d8721e22c63644c55ec35..7657aa897a38e5382d64a4d7504abb50c95ea723 100644 (file)
--- a/arch/powerpc/include/asm/cache.h
+++ b/arch/powerpc/include/asm/cache.h
@@ -20,12 +20,15 @@
 #endif
 #else /* CONFIG_PPC64 */
 #define L1_CACHE_SHIFT         7
+#define IFETCH_ALIGN_SHIFT     4 /* POWER8,9 */
 #endif
 
 #define        L1_CACHE_BYTES          (1 << L1_CACHE_SHIFT)
 
 #define        SMP_CACHE_BYTES         L1_CACHE_BYTES
 
+#define IFETCH_ALIGN_BYTES     (1 << IFETCH_ALIGN_SHIFT)
+
 #if defined(__powerpc64__) && !defined(__ASSEMBLY__)
 struct ppc64_caches {
        u32     dsize;                  /* L1 d-cache size */

diff --git a/arch/powerpc/include/asm/head-64.h b/arch/powerpc/include/asm/head-64.h
index ab90c2fa1ea63215fc969105dc6e8071646ace02..fca7033839a9d7033643895bbe74271a6a31beac 100644 (file)
--- a/arch/powerpc/include/asm/head-64.h
+++ b/arch/powerpc/include/asm/head-64.h
@@ -95,12 +95,12 @@ end_##sname:
 
 #define __FIXED_SECTION_ENTRY_BEGIN(sname, name, __align)      \
        USE_FIXED_SECTION(sname);                               \
-       .align __align;                                         \
+       .balign __align;                                        \
        .global name;                                           \
 name:
 
 #define FIXED_SECTION_ENTRY_BEGIN(sname, name)                 \
-       __FIXED_SECTION_ENTRY_BEGIN(sname, name, 0)
+       __FIXED_SECTION_ENTRY_BEGIN(sname, name, IFETCH_ALIGN_BYTES)
 
 #define FIXED_SECTION_ENTRY_BEGIN_LOCATION(sname, name, start)         \
        USE_FIXED_SECTION(sname);                               \
@@ -203,9 +203,9 @@ name:
 #define EXC_VIRT_END(name, start, end)                 \
        FIXED_SECTION_ENTRY_END_LOCATION(virt_vectors, exc_virt_##start##_##name, end)
 
-#define EXC_COMMON_BEGIN(name)                                 \
+#define EXC_COMMON_BEGIN(name)                                         \
        USE_TEXT_SECTION();                                             \
-       .align  7;                                                      \
+       .balign IFETCH_ALIGN_BYTES;                                     \
        .global name;                                                   \
        DEFINE_FIXED_SYMBOL(name);                                      \
 name:

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 08ba447a4b3dae99676c8b42b8c6deea1866b042..50f0c5ab7e029ef405d7c03cd11e753cc991a96f 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1403,7 +1403,7 @@ USE_TEXT_SECTION()
 /*
  * Hash table stuff
  */
-       .align  7
+       .balign IFETCH_ALIGN_BYTES
 do_hash_page:
 #ifdef CONFIG_PPC_STD_MMU_64
        andis.  r0,r4,0xa410            /* weird error? */