linux-kernel - Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average tracking

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Message-ID: <20140729131957.GE3935@laptop>
Date:	Tue, 29 Jul 2014 15:19:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org, pjt@...gle.com,
	bsegall@...gle.com, arjan.van.de.ven@...el.com,
	len.brown@...el.com, rafael.j.wysocki@...el.com,
	alan.cox@...el.com, mark.gross@...el.com, fengguang.wu@...el.com
Subject: Re: [PATCH 2/2 v4] sched: Rewrite per entity runnable load average
 tracking

On Tue, Jul 29, 2014 at 09:09:45AM +0800, Yuyang Du wrote:
> > > +#define subtract_until_zero(minuend, subtrahend)	\
> > > +	(subtrahend < minuend ? minuend - subtrahend : 0)
> > 
> > WTH is a minuend or subtrahend? Are you a wordsmith in your spare time
> > and like to make up your own words?
> > 
> > Also, isn't writing: x = max(0, x-y), far more readable to begin with?
> > 
> 
> Ok. IIUC, max() does not handle minus number super good, and we don't need the type
> overhead in max(), so still use my macro, but won't be wordsmith again, :)

The 'type' muck is compile time, it doesn't generate any code.

And max() deals just fine with negative numbers assuming you use signed
types, which you could force with max_t().
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