Commit 130d3d68 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

net_sched: psched_ratecfg_precompute() improvements

Before allowing 64bits bytes rates, refactor
psched_ratecfg_precompute() to get better comments
and increased accuracy.

rate_bps field is renamed to rate_bytes_ps, as we only
have to worry about bytes per second.
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Ben Greear <greearb@candelatech.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 45203a3b
...@@ -680,7 +680,7 @@ static inline struct sk_buff *skb_act_clone(struct sk_buff *skb, gfp_t gfp_mask, ...@@ -680,7 +680,7 @@ static inline struct sk_buff *skb_act_clone(struct sk_buff *skb, gfp_t gfp_mask,
#endif #endif
struct psched_ratecfg { struct psched_ratecfg {
u64 rate_bps; u64 rate_bytes_ps; /* bytes per second */
u32 mult; u32 mult;
u16 overhead; u16 overhead;
u8 shift; u8 shift;
...@@ -698,7 +698,7 @@ static inline void psched_ratecfg_getrate(struct tc_ratespec *res, ...@@ -698,7 +698,7 @@ static inline void psched_ratecfg_getrate(struct tc_ratespec *res,
const struct psched_ratecfg *r) const struct psched_ratecfg *r)
{ {
memset(res, 0, sizeof(*res)); memset(res, 0, sizeof(*res));
res->rate = r->rate_bps >> 3; res->rate = r->rate_bytes_ps;
res->overhead = r->overhead; res->overhead = r->overhead;
} }
......
...@@ -901,37 +901,33 @@ void dev_shutdown(struct net_device *dev) ...@@ -901,37 +901,33 @@ void dev_shutdown(struct net_device *dev)
void psched_ratecfg_precompute(struct psched_ratecfg *r, void psched_ratecfg_precompute(struct psched_ratecfg *r,
const struct tc_ratespec *conf) const struct tc_ratespec *conf)
{ {
u64 factor;
u64 mult;
int shift;
memset(r, 0, sizeof(*r)); memset(r, 0, sizeof(*r));
r->overhead = conf->overhead; r->overhead = conf->overhead;
r->rate_bps = (u64)conf->rate << 3; r->rate_bytes_ps = conf->rate;
r->mult = 1; r->mult = 1;
/* /*
* Calibrate mult, shift so that token counting is accurate * The deal here is to replace a divide by a reciprocal one
* for smallest packet size (64 bytes). Token (time in ns) is * in fast path (a reciprocal divide is a multiply and a shift)
* computed as (bytes * 8) * NSEC_PER_SEC / rate_bps. It will *
* work as long as the smallest packet transfer time can be * Normal formula would be :
* accurately represented in nanosec. * time_in_ns = (NSEC_PER_SEC * len) / rate_bps
*/ *
if (r->rate_bps > 0) { * We compute mult/shift to use instead :
/* * time_in_ns = (len * mult) >> shift;
* Higher shift gives better accuracy. Find the largest *
* shift such that mult fits in 32 bits. * We try to get the highest possible mult value for accuracy,
* but have to make sure no overflows will ever happen.
*/ */
for (shift = 0; shift < 16; shift++) { if (r->rate_bytes_ps > 0) {
r->shift = shift; u64 factor = NSEC_PER_SEC;
factor = 8LLU * NSEC_PER_SEC * (1 << r->shift);
mult = div64_u64(factor, r->rate_bps); for (;;) {
if (mult > UINT_MAX) r->mult = div64_u64(factor, r->rate_bytes_ps);
if (r->mult & (1U << 31) || factor & (1ULL << 63))
break; break;
factor <<= 1;
r->shift++;
} }
r->shift = shift - 1;
factor = 8LLU * NSEC_PER_SEC * (1 << r->shift);
r->mult = div64_u64(factor, r->rate_bps);
} }
} }
EXPORT_SYMBOL(psched_ratecfg_precompute); EXPORT_SYMBOL(psched_ratecfg_precompute);
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