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Commit 363ec392 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

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: default avatarEric 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: default avatarDavid S. Miller <davem@davemloft.net>
parent 20d8435a

include/linux/skbuff.h

+57 −2
Original line number Diff line number Diff line
@@ -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;



	union {

		ktime_t		tstamp;

		struct skb_mstamp skb_mstamp;

	};



	struct sock		*sk;

	struct net_device	*dev;