Performance when clearing with string instructions (x86-64-stosq and
similar) can vary significantly based on the chunk-size used.
$ perf bench mem memset -k 4KB -s 4GB -f x86-64-stosq
# Running 'mem/memset' benchmark:
# function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
# Copying 4GB bytes ...
13.748208 GB/sec
$ perf bench mem memset -k 2MB -s 4GB -f x86-64-stosq
# Running 'mem/memset' benchmark:
# function 'x86-64-stosq' (movsq-based memset() in
# arch/x86/lib/memset_64.S)
# Copying 4GB bytes ...
15.067900 GB/sec
$ perf bench mem memset -k 1GB -s 4GB -f x86-64-stosq
# Running 'mem/memset' benchmark:
# function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
# Copying 4GB bytes ...
38.104311 GB/sec
(Both on AMD Milan.)
With a change in chunk-size from 4KB to 1GB, we see the performance go
from 13.7 GB/sec to 38.1 GB/sec. For the chunk-size of 2MB the change isn't
quite as drastic but it is worth adding a clear_page() variant that can
handle contiguous page-extents.
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Tested-by: Raghavendra K T <raghavendra.kt@amd.com>
---
arch/x86/include/asm/page_64.h | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index ec3307234a17..1895c207f629 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -52,8 +52,9 @@ void __clear_pages_unrolled(void *page);
KCFI_REFERENCE(__clear_pages_unrolled);
/**
- * clear_page() - clear a page using a kernel virtual address.
- * @addr: address of kernel page
+ * clear_pages() - clear a page range using a kernel virtual address.
+ * @addr: start address of kernel page range
+ * @npages: number of pages
*
* Switch between three implementations of page clearing based on CPU
* capabilities:
@@ -81,11 +82,11 @@ KCFI_REFERENCE(__clear_pages_unrolled);
*
* Does absolutely no exception handling.
*/
-static inline void clear_page(void *addr)
+static inline void clear_pages(void *addr, unsigned int npages)
{
- u64 len = PAGE_SIZE;
+ u64 len = npages * PAGE_SIZE;
/*
- * Clean up KMSAN metadata for the page being cleared. The assembly call
+ * Clean up KMSAN metadata for the pages being cleared. The assembly call
* below clobbers @addr, so perform unpoisoning before it.
*/
kmsan_unpoison_memory(addr, len);
@@ -106,6 +107,12 @@ static inline void clear_page(void *addr)
: "a" (0)
: "cc", "memory");
}
+#define clear_pages clear_pages
+
+static inline void clear_page(void *addr)
+{
+ clear_pages(addr, 1);
+}
void copy_page(void *to, void *from);
KCFI_REFERENCE(copy_page);
--
2.31.1