linux-kernel - Re: [patch, v2.6.22-rc6] sys

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Date:	Mon, 25 Jun 2007 23:09:46 +0200
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch, v2.6.22-rc6] sys_time() speedup

Hi,

On Monday 25 June 2007, Ingo Molnar wrote:

> the patch improves the sysbench OLTP macrobenchmark significantly:

Has that any real practical relevance?

> @@ -373,6 +376,20 @@ void do_gettimeofday (struct timeval *tv
>
>  	tv->tv_sec = sec;
>  	tv->tv_usec = usec;
> +
> +	/*
> +	 * Make sure xtime.tv_sec [returned by sys_time()] always
> +	 * follows the gettimeofday() result precisely. This
> +	 * condition is extremely unlikely, it can hit at most
> +	 * once per second:
> +	 */
> +	if (unlikely(xtime.tv_sec != tv->tv_sec)) {
> +		unsigned long flags;
> +
> +		write_seqlock_irqsave(&xtime_lock);
> +		update_wall_time();
> +		write_seqlock_irqrestore(&xtime_lock);
> +	}
>  }
>
>  EXPORT_SYMBOL(do_gettimeofday);

Is this the do_gettimeofday() inside CONFIG_TIME_INTERPOLATION?
What did you test?
There can be many ways to read the clock, do you want to put this hook 
everywhere? Wouldn't it be better to improve the clock performance?

bye, Roman
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