net: add skb_mstamp infrastructure
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 <ycheng@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Larry Brakmo <brakmo@google.com> Cc: Julian Anastasov <ja@ssi.bg> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -32,6 +32,7 @@
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#include <linux/hrtimer.h>
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#include <linux/dma-mapping.h>
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#include <linux/netdev_features.h>
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#include <linux/sched.h>
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#include <net/flow_keys.h>
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/* A. Checksumming of received packets by device.
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@ -356,11 +357,62 @@ typedef unsigned int sk_buff_data_t;
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typedef unsigned char *sk_buff_data_t;
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#endif
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/**
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* struct skb_mstamp - multi resolution time stamps
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* @stamp_us: timestamp in us resolution
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* @stamp_jiffies: timestamp in jiffies
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*/
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struct skb_mstamp {
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union {
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u64 v64;
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struct {
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u32 stamp_us;
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u32 stamp_jiffies;
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};
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};
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};
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/**
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* skb_mstamp_get - get current timestamp
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* @cl: place to store timestamps
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*/
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static inline void skb_mstamp_get(struct skb_mstamp *cl)
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{
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u64 val = local_clock();
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do_div(val, NSEC_PER_USEC);
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cl->stamp_us = (u32)val;
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cl->stamp_jiffies = (u32)jiffies;
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}
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/**
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* skb_mstamp_delta - compute the difference in usec between two skb_mstamp
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* @t1: pointer to newest sample
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* @t0: pointer to oldest sample
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*/
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static inline u32 skb_mstamp_us_delta(const struct skb_mstamp *t1,
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const struct skb_mstamp *t0)
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{
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s32 delta_us = t1->stamp_us - t0->stamp_us;
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u32 delta_jiffies = t1->stamp_jiffies - t0->stamp_jiffies;
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/* If delta_us is negative, this might be because interval is too big,
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* or local_clock() drift is too big : fallback using jiffies.
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*/
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if (delta_us <= 0 ||
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delta_jiffies >= (INT_MAX / (USEC_PER_SEC / HZ)))
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delta_us = jiffies_to_usecs(delta_jiffies);
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return delta_us;
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}
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/**
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* struct sk_buff - socket buffer
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* @next: Next buffer in list
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* @prev: Previous buffer in list
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* @tstamp: Time we arrived
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* @tstamp: Time we arrived/left
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* @sk: Socket we are owned by
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* @dev: Device we arrived on/are leaving by
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* @cb: Control buffer. Free for use by every layer. Put private vars here
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@ -429,7 +481,10 @@ struct sk_buff {
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struct sk_buff *next;
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struct sk_buff *prev;
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ktime_t tstamp;
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union {
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ktime_t tstamp;
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struct skb_mstamp skb_mstamp;
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};
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struct sock *sk;
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struct net_device *dev;
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