[PATCH v7 net-next 1/2] net: add skb_mstamp infrastructure
From: Eric Dumazet <hidden>
Date: 2014-02-26 22:02:13
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Eric Dumazet <edumazet@google.com>
ktime_get() is too expensive on some cases, and we'd like to get
usec resolution timestamps in TCP stack.
This patch adds a light weight facility using a combination of
local_clock() and jiffies samples.
Instead of :
u64 t0, t1;
t0 = ktime_get();
// stuff
t1 = ktime_get();
delta_us = ktime_us_delta(t1, t0);
use :
struct skb_mstamp t0, t1;
skb_mstamp_get(&t0);
// stuff
skb_mstamp_get(&t1);
delta_us = skb_mstamp_us_delta(&t1, &t0);
Note : local_clock() might have a (bounded) drift between cpus.
Do not use this infra in place of ktime_get() without understanding the
issues.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: Yuchung Cheng <redacted>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Larry Brakmo <redacted>
Cc: Julian Anastasov <ja@ssi.bg>
---
v7: fix kerneldoc
include/linux/skbuff.h | 59 +++++++++++++++++++++++++++++++++++++--
1 file changed, 57 insertions(+), 2 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 11b6925f0e96..6d8ed22accb4 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h@@ -32,6 +32,7 @@ #include <linux/hrtimer.h> #include <linux/dma-mapping.h> #include <linux/netdev_features.h> +#include <linux/sched.h> #include <net/flow_keys.h> /* A. Checksumming of received packets by device.
@@ -356,11 +357,62 @@ typedef unsigned int sk_buff_data_t; typedef unsigned char *sk_buff_data_t; #endif +/** + * struct skb_mstamp - multi resolution time stamps + * @stamp_us: timestamp in us resolution + * @stamp_jiffies: timestamp in jiffies + */ +struct skb_mstamp { + union { + u64 v64; + struct { + u32 stamp_us; + u32 stamp_jiffies; + }; + }; +}; + +/** + * skb_mstamp_get - get current timestamp + * @cl: place to store timestamps + */ +static inline void skb_mstamp_get(struct skb_mstamp *cl) +{ + u64 val = local_clock(); + + do_div(val, NSEC_PER_USEC); + cl->stamp_us = (u32)val; + cl->stamp_jiffies = (u32)jiffies; +} + +/** + * skb_mstamp_delta - compute the difference in usec between two skb_mstamp + * @t1: pointer to newest sample + * @t0: pointer to oldest sample + */ +static inline u32 skb_mstamp_us_delta(const struct skb_mstamp *t1, + const struct skb_mstamp *t0) +{ + s32 delta_us = t1->stamp_us - t0->stamp_us; + u32 delta_jiffies = t1->stamp_jiffies - t0->stamp_jiffies; + + /* If delta_us is negative, this might be because interval is too big, + * or local_clock() drift is too big : fallback using jiffies. + */ + if (delta_us <= 0 || + delta_jiffies >= (INT_MAX / (USEC_PER_SEC / HZ))) + + delta_us = jiffies_to_usecs(delta_jiffies); + + return delta_us; +} + + /** * struct sk_buff - socket buffer * @next: Next buffer in list * @prev: Previous buffer in list - * @tstamp: Time we arrived + * @tstamp: Time we arrived/left * @sk: Socket we are owned by * @dev: Device we arrived on/are leaving by * @cb: Control buffer. Free for use by every layer. Put private vars here
@@ -429,7 +481,10 @@ struct sk_buff { struct sk_buff *next; struct sk_buff *prev; - ktime_t tstamp; + union { + ktime_t tstamp; + struct skb_mstamp skb_mstamp; + }; struct sock *sk; struct net_device *dev;