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[PATCH] Add cache info to _dl_x86_cpu_features


On Sun, May 8, 2016 at 8:57 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> Support setting processor-specific __x86_shared_non_temporal_threshold
> value in init_cpu_features.
>
> Tested on x86 and x86-64.  Any comments and feebacks?
>
> H.J.
> ---
>         * sysdeps/x86/cacheinfo.c (__x86_shared_non_temporal_threshold):
>         Initialize only if it is zero.
> ---
>  sysdeps/x86/cacheinfo.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c
> index 143b333..788f42d 100644
> --- a/sysdeps/x86/cacheinfo.c
> +++ b/sysdeps/x86/cacheinfo.c
> @@ -669,5 +669,6 @@ init_cacheinfo (void)
>    /* The large memcpy micro benchmark in glibc shows that 6 times of
>       shared cache size is the approximate value above which non-temporal
>       store becomes faster.  */
> -  __x86_shared_non_temporal_threshold = __x86_shared_cache_size * 6;
> +  if (__x86_shared_non_temporal_threshold == 0)
> +    __x86_shared_non_temporal_threshold = __x86_shared_cache_size * 6;
>  }

This doesn't work since init_cpu_features may only update the private copy
in ld.so.  Instead, this patch adds cache info to _dl_x86_cpu_features so
that init_cpu_features sets cache size.

Any comments and feebacks?


-- 
H.J.
From fa82f9be580d9a4be4c3a56cde2aa2b1aadf98fc Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 10 May 2016 05:42:49 -0700
Subject: [PATCH] X86: Add cache info to _dl_x86_cpu_features

This patch adds cache info to _dl_x86_cpu_features to allow a processor
to override cache info derived from CPUID.

Tested on x86 and x86-64.

	* sysdeps/x86/cacheinfo.c: Skip if not in libc.
	(init_cacheinfo): Use raw_data_size, raw_shared_size and
	shared_non_temporal_threshold from _dl_x86_cpu_features if
	not zero.
	* sysdeps/x86/cpu-features.h (cache_info): New.
	(cpu_features): Add cache.
---
 sysdeps/x86/cacheinfo.c    | 17 ++++++++++++++++-
 sysdeps/x86/cpu-features.h | 13 +++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/sysdeps/x86/cacheinfo.c b/sysdeps/x86/cacheinfo.c
index 143b333..d6d0083 100644
--- a/sysdeps/x86/cacheinfo.c
+++ b/sysdeps/x86/cacheinfo.c
@@ -16,6 +16,8 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+#if IS_IN (libc)
+
 #include <assert.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -646,6 +648,11 @@ init_cacheinfo (void)
 #endif
     }
 
+  const struct cache_info *cache = &GLRO(dl_x86_cpu_features).cache;
+
+  if (cache->raw_data_size != 0)
+    data = cache->raw_data_size;
+
   if (data > 0)
     {
       __x86_raw_data_cache_size_half = data / 2;
@@ -656,6 +663,9 @@ init_cacheinfo (void)
       __x86_data_cache_size = data;
     }
 
+  if (cache->raw_shared_size != 0)
+    shared = cache->raw_shared_size;
+
   if (shared > 0)
     {
       __x86_raw_shared_cache_size_half = shared / 2;
@@ -669,5 +679,10 @@ init_cacheinfo (void)
   /* The large memcpy micro benchmark in glibc shows that 6 times of
      shared cache size is the approximate value above which non-temporal
      store becomes faster.  */
-  __x86_shared_non_temporal_threshold = __x86_shared_cache_size * 6;
+  __x86_shared_non_temporal_threshold
+    = (cache->shared_non_temporal_threshold != 0
+       ? cache->shared_non_temporal_threshold
+       : __x86_shared_cache_size * 6);
 }
+
+#endif
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index 9529d61..335d96a 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -164,6 +164,18 @@
 
 #else	/* __ASSEMBLER__ */
 
+struct cache_info
+{
+  /* Data cache size for use in memory and string routines, typically
+     L1 size.  */
+  long int raw_data_size;
+  /* Shared cache size for use in memory and string routines, typically
+     L2 or L3 size.  */
+  long int raw_shared_size;
+  /* Threshold to use non temporal store.  */
+  long int shared_non_temporal_threshold;
+};
+
 enum
   {
     COMMON_CPUID_INDEX_1 = 0,
@@ -193,6 +205,7 @@ struct cpu_features
   unsigned int family;
   unsigned int model;
   unsigned int feature[FEATURE_INDEX_MAX];
+  struct cache_info cache;
 };
 
 /* Used from outside of glibc to get access to the CPU features
-- 
2.5.5


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