netdev - Re: [PATCH v7 net-next 1/2] net: add skb

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Message-Id: <20140226.170425.1796947766908119120.davem@davemloft.net>
Date:	Wed, 26 Feb 2014 17:04:25 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ja@....bg, ycheng@...gle.com, netdev@...r.kernel.org,
	ncardwell@...gle.com, brakmo@...gle.com, stephen@...workplumber.org
Subject: Re: [PATCH v7 net-next 1/2] net: add skb_mstamp infrastructure

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 26 Feb 2014 14:02:11 -0800

> From: Eric Dumazet <edumazet@...gle.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@...gle.com>

Applied.
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