| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Thu, 06 Jun 2013 13:56:19 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Ben Greear <greearb@...delatech.com>
Cc: David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: [PATCH v2 net-next] net_sched: psched_ratecfg_precompute()
improvements
From: Eric Dumazet <edumazet@...gle.com>
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: Eric Dumazet <edumazet@...gle.com>
Cc: Ben Greear <greearb@...delatech.com>
---
v2: rate_bps renamed to rate_bytes_ps (Ben Greear)
include/net/sch_generic.h | 4 +--
net/sched/sch_generic.c | 44 ++++++++++++++++--------------------
2 files changed, 22 insertions(+), 26 deletions(-)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index e7f4e21..9485428 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -679,7 +679,7 @@ static inline struct sk_buff *skb_act_clone(struct sk_buff *skb, gfp_t gfp_mask,
#endif
struct psched_ratecfg {
- u64 rate_bps;
+ u64 rate_bytes_ps; /* bytes per second */
u32 mult;
u16 overhead;
u8 shift;
@@ -697,7 +697,7 @@ static inline void psched_ratecfg_getrate(struct tc_ratespec *res,
const struct psched_ratecfg *r)
{
memset(res, 0, sizeof(*res));
- res->rate = r->rate_bps >> 3;
+ res->rate = r->rate_bytes_ps;
res->overhead = r->overhead;
}
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 2022408..4626cef 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -901,37 +901,33 @@ void dev_shutdown(struct net_device *dev)
void psched_ratecfg_precompute(struct psched_ratecfg *r,
const struct tc_ratespec *conf)
{
- u64 factor;
- u64 mult;
- int shift;
-
memset(r, 0, sizeof(*r));
r->overhead = conf->overhead;
- r->rate_bps = (u64)conf->rate << 3;
+ r->rate_bytes_ps = conf->rate;
r->mult = 1;
/*
- * Calibrate mult, shift so that token counting is accurate
- * for smallest packet size (64 bytes). Token (time in ns) is
- * computed as (bytes * 8) * NSEC_PER_SEC / rate_bps. It will
- * work as long as the smallest packet transfer time can be
- * accurately represented in nanosec.
+ * The deal here is to replace a divide by a reciprocal one
+ * in fast path (a reciprocal divide is a multiply and a shift)
+ *
+ * Normal formula would be :
+ * time_in_ns = (NSEC_PER_SEC * len) / rate_bps
+ *
+ * We compute mult/shift to use instead :
+ * time_in_ns = (len * mult) >> shift;
+ *
+ * We try to get the highest possible mult value for accuracy,
+ * but have to make sure no overflows will ever happen.
*/
- if (r->rate_bps > 0) {
- /*
- * Higher shift gives better accuracy. Find the largest
- * shift such that mult fits in 32 bits.
- */
- for (shift = 0; shift < 16; shift++) {
- r->shift = shift;
- factor = 8LLU * NSEC_PER_SEC * (1 << r->shift);
- mult = div64_u64(factor, r->rate_bps);
- if (mult > UINT_MAX)
+ if (r->rate_bytes_ps > 0) {
+ u64 factor = NSEC_PER_SEC;
+
+ for (;;) {
+ r->mult = div64_u64(factor, r->rate_bytes_ps);
+ if (r->mult & (1U << 31) || factor & (1ULL << 63))
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);
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists