File datapath-compat-downstream-the-reciprocal_div.patch of Package openvswitch.6050
From a27ce57b65959a3fb796ebb20958930624b0732e Mon Sep 17 00:00:00 2001
From: Alex Wang <alexw@nicira.com>
Date: Fri, 14 Mar 2014 11:47:30 -0700
Subject: [PATCH] datapath: compat: Downstream the reciprocal_div.{c,h}.
The reciprocal division code used in datapath is flawed. The bug
has been fixed in the linux kernel repo in commit 809fa972fd(
reciprocal_divide: update/correction of the algorithm).
This commit downstreams the reciprocal_div.{c,h} from the linux
kernel repo.
Signed-off-by: Alex Wang <alexw@nicira.com>
Reviewed-by: Thomas Graf <tgraf@redhat.com>
Acked-by: Pravin B Shelar <pshelar@nicira.com>
---
datapath/linux/Modules.mk | 1 +
datapath/linux/compat/flex_array.c | 2 +-
datapath/linux/compat/include/linux/flex_array.h | 3 +-
.../linux/compat/include/linux/reciprocal_div.h | 37 ++++++++++++++++++++
datapath/linux/compat/reciprocal_div.c | 28 ++++++++++-----
5 files changed, 61 insertions(+), 10 deletions(-)
create mode 100644 datapath/linux/compat/include/linux/reciprocal_div.h
diff --git a/datapath/linux/Modules.mk b/datapath/linux/Modules.mk
index cedb8c9..1e76305 100644
--- a/datapath/linux/Modules.mk
+++ b/datapath/linux/Modules.mk
@@ -47,6 +47,7 @@ openvswitch_headers += \
linux/compat/include/linux/poison.h \
linux/compat/include/linux/rculist.h \
linux/compat/include/linux/rcupdate.h \
+ linux/compat/include/linux/reciprocal_div.h \
linux/compat/include/linux/rtnetlink.h \
linux/compat/include/linux/skbuff.h \
linux/compat/include/linux/slab.h \
diff --git a/datapath/linux/compat/flex_array.c b/datapath/linux/compat/flex_array.c
index 1e6d9c1..c39dd1b 100644
--- a/datapath/linux/compat/flex_array.c
+++ b/datapath/linux/compat/flex_array.c
@@ -93,8 +93,8 @@ struct flex_array *flex_array_alloc(int element_size, unsigned int total,
gfp_t flags)
{
struct flex_array *ret;
+ struct reciprocal_value reciprocal_elems = {0};
int elems_per_part = 0;
- int reciprocal_elems = 0;
int max_size = 0;
if (element_size) {
diff --git a/datapath/linux/compat/include/linux/flex_array.h b/datapath/linux/compat/include/linux/flex_array.h
index 1cc6648..443c4af 100644
--- a/datapath/linux/compat/include/linux/flex_array.h
+++ b/datapath/linux/compat/include/linux/flex_array.h
@@ -6,6 +6,7 @@
#include_next <linux/flex_array.h>
#else
+#include <linux/reciprocal_div.h>
#include <linux/types.h>
#include <asm/page.h>
@@ -27,7 +28,7 @@ struct flex_array {
int element_size;
int total_nr_elements;
int elems_per_part;
- u32 reciprocal_elems;
+ struct reciprocal_value reciprocal_elems;
struct flex_array_part *parts[];
};
/*
diff --git a/datapath/linux/compat/include/linux/reciprocal_div.h b/datapath/linux/compat/include/linux/reciprocal_div.h
new file mode 100644
index 0000000..2def5c6
--- /dev/null
+++ b/datapath/linux/compat/include/linux/reciprocal_div.h
@@ -0,0 +1,37 @@
+#ifndef _LINUX_RECIPROCAL_DIV_WRAPPER_H
+#define _LINUX_RECIPROCAL_DIV_WRAPPER_H 1
+
+#include <linux/types.h>
+
+/*
+ * This algorithm is based on the paper "Division by Invariant
+ * Integers Using Multiplication" by Torbjörn Granlund and Peter
+ * L. Montgomery.
+ *
+ * The assembler implementation from Agner Fog, which this code is
+ * based on, can be found here:
+ * http://www.agner.org/optimize/asmlib.zip
+ *
+ * This optimization for A/B is helpful if the divisor B is mostly
+ * runtime invariant. The reciprocal of B is calculated in the
+ * slow-path with reciprocal_value(). The fast-path can then just use
+ * a much faster multiplication operation with a variable dividend A
+ * to calculate the division A/B.
+ */
+
+#define reciprocal_value rpl_reciprocal_value
+struct reciprocal_value {
+ u32 m;
+ u8 sh1, sh2;
+};
+
+struct reciprocal_value reciprocal_value(u32 d);
+
+#define reciprocal_divide rpl_reciprocal_divide
+static inline u32 reciprocal_divide(u32 a, struct reciprocal_value R)
+{
+ u32 t = (u32)(((u64)a * R.m) >> 32);
+ return (t + ((a - t) >> R.sh1)) >> R.sh2;
+}
+
+#endif /* _LINUX_RECIPROCAL_DIV_WRAPPER_H */
diff --git a/datapath/linux/compat/reciprocal_div.c b/datapath/linux/compat/reciprocal_div.c
index 7ec7528..90ce7b1 100644
--- a/datapath/linux/compat/reciprocal_div.c
+++ b/datapath/linux/compat/reciprocal_div.c
@@ -1,13 +1,25 @@
+#include <linux/kernel.h>
#include <asm/div64.h>
#include <linux/reciprocal_div.h>
-#include <linux/version.h>
-#if LINUX_VERSION_CODE < KERNEL_VERSION(3,3,0)
-/* definition is required since reciprocal_value() is not exported */
-u32 reciprocal_value(u32 k)
+/*
+ * For a description of the algorithm please have a look at
+ * include/linux/reciprocal_div.h
+ */
+
+struct reciprocal_value reciprocal_value(u32 d)
{
- u64 val = (1LL << 32) + (k - 1);
- do_div(val, k);
- return (u32)val;
+ struct reciprocal_value R;
+ u64 m;
+ int l;
+
+ l = fls(d - 1);
+ m = ((1ULL << 32) * ((1ULL << l) - d));
+ do_div(m, d);
+ ++m;
+ R.m = (u32)m;
+ R.sh1 = min(l, 1);
+ R.sh2 = max(l - 1, 0);
+
+ return R;
}
-#endif
--
1.7.9.5
