linux-kernel - Re: [PATCH v7 03/17] tracing: add MIPS specific trace_clock

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Message-ID: <4AF9A77E.6020908@caviumnetworks.com>
Date:	Tue, 10 Nov 2009 09:48:46 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Wu Zhangjin <wuzhangjin@...il.com>
CC:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	zhangfx@...ote.com, zhouqg@...il.com,
	Ralf Baechle <ralf@...ux-mips.org>, rostedt@...dmis.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Nicholas Mc Guire <der.herr@...r.at>,
	Richard Sandiford <rdsandiford@...glemail.com>,
	Patrik Kluba <kpajko79@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michal Simek <monstr@...str.eu>
Subject: Re: [PATCH v7 03/17] tracing: add MIPS specific trace_clock_local()

Wu Zhangjin wrote:
[...]
> + * trace_clock_local(): the simplest and least coherent tracing clock.
> + *
> + * Useful for tracing that does not cross to other CPUs nor
> + * does it go through idle events.
> + */
> +u64 trace_clock_local(void)
> +{
> +	unsigned long flags;
> +	u64 clock;
> +
> +	raw_local_irq_save(flags);
> +
> +	clock = mips_timecounter_read();
> +
> +	raw_local_irq_restore(flags);
> +
> +	return clock;
> +}

Why disable interrupts?

Also you call the new function mips_timecounter_read().  Since 
sched_clock() is a weak function, you can override the definition with a 
more accurate version when possible.  Then you could just directly call 
it here, instead of adding the new mips_timecounter_read() that the 
'[PATCH v7 02/17] tracing: add mips_timecounter_read() for MIPS' adds.

David Daney
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