linux-kernel - Re: [RFC PATCH 10/11] time sync: generic infrastructure to map between time stamps generated by a clock source and system time

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Message-Id: <20081119171445.bd02498e.akpm@linux-foundation.org>
Date:	Wed, 19 Nov 2008 17:14:45 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Patrick Ohly <patrick.ohly@...el.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	davem@...emloft.net, patrick.ohly@...el.com
Subject: Re: [RFC PATCH 10/11] time sync: generic infrastructure to map
 between time stamps generated by a clock source and system time


These patcehs add a lot of quite large inlined functions.

On Wed, 19 Nov 2008 13:08:47 +0100
Patrick Ohly <patrick.ohly@...el.com> wrote:

> +static inline void clocksync_update(struct clocksync *sync,
> +			u64 hwtstamp)
> +{
> +	s64 offset;
> +	u64 average_time;
> +
> +	if (hwtstamp &&
> +		(s64)(hwtstamp - sync->last_update) < NSEC_PER_SEC)
> +		return;
> +
> +	if (!clocksync_offset(sync, &offset, &average_time))
> +		return;
> +
> +	printk(KERN_DEBUG
> +		"average offset: %lld\n", offset);
> +
> +	if (!sync->last_update) {
> +		sync->last_update = average_time;
> +		sync->offset = offset;
> +		sync->skew = 0;
> +	} else {
> +		s64 delta_nsec = average_time - sync->last_update;
> +
> +		/* avoid division by negative or small deltas */
> +		if (delta_nsec >= 10000) {
> +			s64 delta_offset_nsec = offset - sync->offset;
> +			s64 skew = delta_offset_nsec *
> +				CLOCKSYNC_SKEW_RESOLUTION /
> +				delta_nsec;
> +
> +			/**
> +			 * Calculate new overall skew as 4/16 the
> +			 * old value and 12/16 the new one. This is
> +			 * a rather arbitrary tradeoff between
> +			 * only using the latest measurement (0/16 and
> +			 * 16/16) and even more weight on past measurements.
> +			 */
> +#define CLOCKSYNC_NEW_SKEW_PER_16 12
> +			sync->skew =
> +				((16 - CLOCKSYNC_NEW_SKEW_PER_16) * sync->skew +
> +					CLOCKSYNC_NEW_SKEW_PER_16 * skew) /
> +				16;
> +			sync->last_update = average_time;
> +			sync->offset = offset;
> +		}
> +	}
> +}

This one is a champ.

The token '/**' is used exclusively to introduce kerneldoc-formatted
comments.  Please check the patches for comments which are incorrectly
thus-tagged.

Please cc linux-api@...r.kernel.org on patches which affect the
kernel's userspace interfaces.

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