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Date: Fri, 23 Jan 2015 15:28:25 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Jones <davej@codemonkey.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Richard Cochran <richardcochran@gmail.com>,
        Prarit Bhargava <prarit@redhat.com>,
        Stephen Boyd <sboyd@codeaurora.org>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 06/12] time: Add infrastructure to cap clocksource reads
 to the max_cycles value
Message-ID: <20150123142825.GB23123@twins.programming.kicks-ass.net>
References: <1421971767-17707-1-git-send-email-john.stultz@linaro.org>
 <1421971767-17707-7-git-send-email-john.stultz@linaro.org>
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On Thu, Jan 22, 2015 at 04:09:21PM -0800, John Stultz wrote:
> +static inline cycle_t timekeeping_get_delta(struct tk_read_base *tkr)
> +{
> +	cycle_t cycle_now, delta;
> +
> +	/* read clocksource */
> +	cycle_now = tkr->read(tkr->clock);
> +
> +	/* calculate the delta since the last update_wall_time */
> +	delta = clocksource_delta(cycle_now, tkr->cycle_last, tkr->mask);
> +
> +	/* Cap delta value to the max_cycles values to avoid mult overflows */
> +	if (unlikely(delta > tkr->clock->max_cycles))
> +		delta = tkr->clock->max_cycles;


Should we not raise _something_ here? I know we cannot printk() here,
but bad (TM) things happened if this ever triggers.

> +
> +	return delta;
> +}