Re: [PATCH 2/3] genirq/timings: Add array suffix computation code

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: rjw@rjwysocki.net, ulf.hansson@linaro.org,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] genirq/timings: Add array suffix computation code
Date: Tue, 26 Mar 2019 16:22:59 +0100	[thread overview]
Message-ID: <5ad6f7d7-3081-8eef-1adf-3ce705a1ba94@linaro.org> (raw)
In-Reply-To: <alpine.DEB.2.21.1903241825210.1798@nanos.tec.linutronix.de>

Hi Thomas,

thanks for reviewing this patch.

[ ... ]

>> +
>> +/*
>> + * Exponential moving average computation
>> + */
>> +static int irq_timings_ema_new(s64 value, s64 ema_old)
> 
> There is a mixed bag of s64/u64 all over this code. Please stay
> consistent. We had enough sign confusion bugs in the past.

Right.

I have a question, ema_old and value will be always u64 type and the
function irq_timings_ema_new() will return an u64 ...

> 	value = (value - ema_old) * EMA_ALPHA_VAL;
> 	return ema_old + value >> EMA_ALPHA_SHIFT;

... how can I deal with the operations above when value < ema_old ?

Shall I use an intermediate s64 ?

eg:

	s64 aux = (value - ema_old) * EMA_ALPHA_VAL;
	return ema_old + aux >> EMA_ALPHA_SHIFT;
?

[ ... ]

 > Other than that this looks good to me. Nice work!

Thanks, I appreciate.

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