[ARM] alternative copy_to_user: more precise fallback threshold

[safe/jmp/linux-2.6] / arch / arm / lib / uaccess_with_memcpy.c

diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
index 92838e7..6b967ff 100644 (file)
--- a/arch/arm/lib/uaccess_with_memcpy.c
+++ b/arch/arm/lib/uaccess_with_memcpy.c
@@ -106,7 +106,7 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
         * With frame pointer disabled, tail call optimization kicks in
         * as well making this test almost invisible.
         */
-       if (n < 1024)
+       if (n < 64)
                return __copy_to_user_std(to, from, n);
        return __copy_to_user_memcpy(to, from, n);
 }
@@ -151,7 +151,78 @@ out:
 unsigned long __clear_user(void __user *addr, unsigned long n)
 {
        /* See rational for this in __copy_to_user() above. */
-       if (n < 256)
+       if (n < 64)
                return __clear_user_std(addr, n);
        return __clear_user_memset(addr, n);
 }
+
+#if 0
+
+/*
+ * This code is disabled by default, but kept around in case the chosen
+ * thresholds need to be revalidated.  Some overhead (small but still)
+ * would be implied by a runtime determined variable threshold, and
+ * so far the measurement on concerned targets didn't show a worthwhile
+ * variation.
+ *
+ * Note that a fairly precise sched_clock() implementation is needed
+ * for results to make some sense.
+ */
+
+#include <linux/vmalloc.h>
+
+static int __init test_size_treshold(void)
+{
+       struct page *src_page, *dst_page;
+       void *user_ptr, *kernel_ptr;
+       unsigned long long t0, t1, t2;
+       int size, ret;
+
+       ret = -ENOMEM;
+       src_page = alloc_page(GFP_KERNEL);
+       if (!src_page)
+               goto no_src;
+       dst_page = alloc_page(GFP_KERNEL);
+       if (!dst_page)
+               goto no_dst;
+       kernel_ptr = page_address(src_page);
+       user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
+       if (!user_ptr)
+               goto no_vmap;
+
+       /* warm up the src page dcache */
+       ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
+
+       for (size = PAGE_SIZE; size >= 4; size /= 2) {
+               t0 = sched_clock();
+               ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
+               t1 = sched_clock();
+               ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
+               t2 = sched_clock();
+               printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
+       }
+
+       for (size = PAGE_SIZE; size >= 4; size /= 2) {
+               t0 = sched_clock();
+               ret |= __clear_user_memset(user_ptr, size);
+               t1 = sched_clock();
+               ret |= __clear_user_std(user_ptr, size);
+               t2 = sched_clock();
+               printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
+       }
+
+       if (ret)
+               ret = -EFAULT;
+
+       vunmap(user_ptr);
+no_vmap:
+       put_page(dst_page);
+no_dst:
+       put_page(src_page);
+no_src:
+       return ret;
+}
+
+subsys_initcall(test_size_treshold);
+
+#endif