linux-kernel - Re: [PATCH 1/4] Add clock_gettime

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Message-ID: <4EFB67AB.7060707@fb.com>
Date:	Wed, 28 Dec 2011 11:02:03 -0800
From:	Arun Sharma <asharma@...com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	<linux-kernel@...r.kernel.org>, Kumar Sundararajan <kumar@...com>,
	john stultz <johnstul@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH 1/4] Add clock_gettime_ns syscall

On 12/25/11 8:51 AM, Andy Lutomirski wrote:

> +struct timens {
> +	u64	ns;		/* nanoseconds since the relevant epoch */
> +	u64	padding;	/* for future expansion (UTC offset? sub-ns?) */
> +};
>..
> +SYSCALL_DEFINE2(clock_gettime_ns, const clockid_t, which_clock,
> +		struct timens __user *, tp)
> +{

How about returning a (signed) long as the time in ns? This way, we save 
a store and a load and the value can be passed in registers.

This shouldn't preclude future expansion via extra args.

  -Arun
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