[PATCH v2 09/14] x86/clear_page: add arch_clear_page_uncached_threshold()

[Ankur Arora <ankur.a.arora@oracle.com>]

Add arch_clear_page_uncached_threshold() for a machine specific value
above which clear_page_uncached() would be used.

The ideal threshold value depends on the CPU model and where the
performance curves for cached and uncached stores intersect.
A safe value is LLC-size, so we use that of the boot_cpu.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/x86/include/asm/cacheinfo.h |  1 +
 arch/x86/kernel/cpu/cacheinfo.c  | 13 +++++++++++++
 arch/x86/kernel/setup.c          |  6 ++++++
 3 files changed, 20 insertions(+)

diff --git a/arch/x86/include/asm/cacheinfo.h b/arch/x86/include/asm/cacheinfo.h
index 86b2e0dcc4bf..5c6045699e94 100644
--- a/arch/x86/include/asm/cacheinfo.h
+++ b/arch/x86/include/asm/cacheinfo.h
@@ -4,5 +4,6 @@
 
 void cacheinfo_amd_init_llc_id(struct cpuinfo_x86 *c, int cpu);
 void cacheinfo_hygon_init_llc_id(struct cpuinfo_x86 *c, int cpu);
+int cacheinfo_lookup_max_size(int cpu);
 
 #endif /* _ASM_X86_CACHEINFO_H */
diff --git a/arch/x86/kernel/cpu/cacheinfo.c b/arch/x86/kernel/cpu/cacheinfo.c
index b5e36bd0425b..6c34fc22d9ae 100644
--- a/arch/x86/kernel/cpu/cacheinfo.c
+++ b/arch/x86/kernel/cpu/cacheinfo.c
@@ -1033,3 +1033,16 @@ int populate_cache_leaves(unsigned int cpu)
 
 	return 0;
 }
+
+int cacheinfo_lookup_max_size(int cpu)
+{
+	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
+	struct cacheinfo *this_leaf = this_cpu_ci->info_list;
+	struct cacheinfo *max_leaf;
+
+	/*
+	 * Assume that cache sizes always increase with level.
+	 */
+	max_leaf = this_leaf + this_cpu_ci->num_leaves - 1;
+	return max_leaf->size;
+}
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 40ed44ead063..1b3e2c40f832 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -49,6 +49,7 @@
 #include <asm/thermal.h>
 #include <asm/unwind.h>
 #include <asm/vsyscall.h>
+#include <asm/cacheinfo.h>
 #include <linux/vmalloc.h>
 
 /*
@@ -1250,3 +1251,8 @@ static int __init register_kernel_offset_dumper(void)
 	return 0;
 }
 __initcall(register_kernel_offset_dumper);
+
+unsigned long __init arch_clear_page_uncached_threshold(void)
+{
+	return cacheinfo_lookup_max_size(0);
+}
-- 
2.29.2