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

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Date:   Tue, 26 Mar 2019 16:22:59 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     rjw@...ysocki.net, ulf.hansson@...aro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] genirq/timings: Add array suffix computation code


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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