diff options
| -rw-r--r-- | include/net/codel.h | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/include/net/codel.h b/include/net/codel.h index bd8747c3ba6..7546517326b 100644 --- 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 codel_stats *stats) * 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(codel_time_t t, 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(struct Qdisc *sch, 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, |