kernel: add codel and fq_codel to generic 3.3 patch set (based on patch by Dave Täht)

[openwrt/svn-archive/archive.git] / target / linux / generic / patches-3.3 / 045-codel-use-u16-field-instead-of-31bits-for-rec_inv_sq.patch

diff --git a/target/linux/generic/patches-3.3/045-codel-use-u16-field-instead-of-31bits-for-rec_inv_sq.patch b/target/linux/generic/patches-3.3/045-codel-use-u16-field-instead-of-31bits-for-rec_inv_sq.patch
new file mode 100644 (file)
index 0000000..814aebc
--- /dev/null
+++ b/target/linux/generic/patches-3.3/045-codel-use-u16-field-instead-of-31bits-for-rec_inv_sq.patch
@@ -0,0 +1,85 @@
+From 6ff272c9ad65eda219cd975b9da2dbc31cc812ee Mon Sep 17 00:00:00 2001
+From: Eric Dumazet <eric.dumazet@gmail.com>
+Date: Sat, 12 May 2012 21:23:23 +0000
+Subject: [PATCH 46/50] codel: use u16 field instead of 31bits for
+ rec_inv_sqrt
+
+David pointed out gcc might generate poor code with 31bit fields.
+
+Using u16 is more than enough and permits a better code output.
+
+Also make the code intent more readable using constants, fixed point arithmetic
+not being trivial for everybody.
+
+Suggested-by: David Miller <davem@davemloft.net>
+Signed-off-by: Eric Dumazet <edumazet@google.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+---
+ include/net/codel.h |   25 +++++++++++++++----------
+ 1 file changed, 15 insertions(+), 10 deletions(-)
+
+--- a/include/net/codel.h
++++ b/include/net/codel.h
+@@ -133,13 +133,17 @@ struct codel_params {
+ struct codel_vars {
+       u32             count;
+       u32             lastcount;
+-      bool            dropping:1;
+-      u32             rec_inv_sqrt:31;
++      bool            dropping;
++      u16             rec_inv_sqrt;
+       codel_time_t    first_above_time;
+       codel_time_t    drop_next;
+       codel_time_t    ldelay;
+ };
+ 
++#define REC_INV_SQRT_BITS (8 * sizeof(u16)) /* or sizeof_in_bits(rec_inv_sqrt) */
++/* needed shift to get a Q0.32 number from rec_inv_sqrt */
++#define REC_INV_SQRT_SHIFT (32 - REC_INV_SQRT_BITS)
++
+ /**
+  * struct codel_stats - contains codel shared variables and stats
+  * @maxpacket:        largest packet we've seen so far
+@@ -173,17 +177,18 @@ static void codel_stats_init(struct code
+  * http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Iterative_methods_for_reciprocal_square_roots
+  * new_invsqrt = (invsqrt / 2) * (3 - count * invsqrt^2)
+  *
+- * Here, invsqrt is a fixed point number (< 1.0), 31bit mantissa)
++ * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32
+  */
+ static void codel_Newton_step(struct codel_vars *vars)
+ {
+-      u32 invsqrt = vars->rec_inv_sqrt;
+-      u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 31;
+-      u64 val = (3LL << 31) - ((u64)vars->count * invsqrt2);
++      u32 invsqrt = ((u32)vars->rec_inv_sqrt) << REC_INV_SQRT_SHIFT;
++      u32 invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;
++      u64 val = (3LL << 32) - ((u64)vars->count * invsqrt2);
+ 
+-      val = (val * invsqrt) >> 32;
++      val >>= 2; /* avoid overflow in following multiply */
++      val = (val * invsqrt) >> (32 - 2 + 1);
+ 
+-      vars->rec_inv_sqrt = val;
++      vars->rec_inv_sqrt = val >> REC_INV_SQRT_SHIFT;
+ }
+ 
+ /*
+@@ -195,7 +200,7 @@ static codel_time_t codel_control_law(co
+                                     codel_time_t interval,
+                                     u32 rec_inv_sqrt)
+ {
+-      return t + reciprocal_divide(interval, rec_inv_sqrt << 1);
++      return t + reciprocal_divide(interval, rec_inv_sqrt << REC_INV_SQRT_SHIFT);
+ }
+ 
+ 
+@@ -326,7 +331,7 @@ static struct sk_buff *codel_dequeue(str
+                       codel_Newton_step(vars);
+               } else {
+                       vars->count = 1;
+-                      vars->rec_inv_sqrt = 0x7fffffff;
++                      vars->rec_inv_sqrt = ~0U >> REC_INV_SQRT_SHIFT;
+               }
+               vars->lastcount = vars->count;
+               vars->drop_next = codel_control_law(now, params->interval,