percpu: add test module for various percpu operations

Tests various percpu operations.

Enable with CONFIG_PERCPU_TEST=m.

Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 138 insertions, 0 deletions

diff --git a/lib/percpu_test.c b/lib/percpu_test.c
new file mode 100644
index 000000000000..0b5d14dadd1a
--- /dev/null
+++ b/lib/percpu_test.c
@@ -0,0 +1,138 @@
+#include <linux/module.h>
+
+/* validate @native and @pcp counter values match @expected */
+#define CHECK(native, pcp, expected)                                    \
+        do {                                                            \
+                WARN((native) != (expected),                            \
+                     "raw %ld (0x%lx) != expected %lld (0x%llx)",       \
+                     (native), (native),                                \
+                     (long long)(expected), (long long)(expected));     \
+                WARN(__this_cpu_read(pcp) != (expected),                \
+                     "pcp %ld (0x%lx) != expected %lld (0x%llx)",       \
+                     __this_cpu_read(pcp), __this_cpu_read(pcp),        \
+                     (long long)(expected), (long long)(expected));     \
+        } while (0)
+
+static DEFINE_PER_CPU(long, long_counter);
+static DEFINE_PER_CPU(unsigned long, ulong_counter);
+
+static int __init percpu_test_init(void)
+{
+        /*
+         * volatile prevents compiler from optimizing it uses, otherwise the
+         * +ul_one/-ul_one below would replace with inc/dec instructions.
+         */
+        volatile unsigned int ui_one = 1;
+        long l = 0;
+        unsigned long ul = 0;
+
+        pr_info("percpu test start\n");
+
+        preempt_disable();
+
+        l += -1;
+        __this_cpu_add(long_counter, -1);
+        CHECK(l, long_counter, -1);
+
+        l += 1;
+        __this_cpu_add(long_counter, 1);
+        CHECK(l, long_counter, 0);
+
+        ul = 0;
+        __this_cpu_write(ulong_counter, 0);
+
+        ul += 1UL;
+        __this_cpu_add(ulong_counter, 1UL);
+        CHECK(ul, ulong_counter, 1);
+
+        ul += -1UL;
+        __this_cpu_add(ulong_counter, -1UL);
+        CHECK(ul, ulong_counter, 0);
+
+        ul += -(unsigned long)1;
+        __this_cpu_add(ulong_counter, -(unsigned long)1);
+        CHECK(ul, ulong_counter, -1);
+
+        ul = 0;
+        __this_cpu_write(ulong_counter, 0);
+
+        ul -= 1;
+        __this_cpu_dec(ulong_counter);
+        CHECK(ul, ulong_counter, -1);
+        CHECK(ul, ulong_counter, ULONG_MAX);
+
+        l += -ui_one;
+        __this_cpu_add(long_counter, -ui_one);
+        CHECK(l, long_counter, 0xffffffff);
+
+        l += ui_one;
+        __this_cpu_add(long_counter, ui_one);
+        CHECK(l, long_counter, (long)0x100000000LL);
+
+
+        l = 0;
+        __this_cpu_write(long_counter, 0);
+
+        l -= ui_one;
+        __this_cpu_sub(long_counter, ui_one);
+        CHECK(l, long_counter, -1);
+
+        l = 0;
+        __this_cpu_write(long_counter, 0);
+
+        l += ui_one;
+        __this_cpu_add(long_counter, ui_one);
+        CHECK(l, long_counter, 1);
+
+        l += -ui_one;
+        __this_cpu_add(long_counter, -ui_one);
+        CHECK(l, long_counter, (long)0x100000000LL);
+
+        l = 0;
+        __this_cpu_write(long_counter, 0);
+
+        l -= ui_one;
+        this_cpu_sub(long_counter, ui_one);
+        CHECK(l, long_counter, -1);
+        CHECK(l, long_counter, ULONG_MAX);
+
+        ul = 0;
+        __this_cpu_write(ulong_counter, 0);
+
+        ul += ui_one;
+        __this_cpu_add(ulong_counter, ui_one);
+        CHECK(ul, ulong_counter, 1);
+
+        ul = 0;
+        __this_cpu_write(ulong_counter, 0);
+
+        ul -= ui_one;
+        __this_cpu_sub(ulong_counter, ui_one);
+        CHECK(ul, ulong_counter, -1);
+        CHECK(ul, ulong_counter, ULONG_MAX);
+
+        ul = 3;
+        __this_cpu_write(ulong_counter, 3);
+
+        ul = this_cpu_sub_return(ulong_counter, ui_one);
+        CHECK(ul, ulong_counter, 2);
+
+        ul = __this_cpu_sub_return(ulong_counter, ui_one);
+        CHECK(ul, ulong_counter, 1);
+
+        preempt_enable();
+
+        pr_info("percpu test done\n");
+        return -EAGAIN;  /* Fail will directly unload the module */
+}
+
+static void __exit percpu_test_exit(void)
+{
+}
+
+module_init(percpu_test_init)
+module_exit(percpu_test_exit)
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Greg Thelen");
+MODULE_DESCRIPTION("percpu operations test");