linux-kernel - Re: [PATCH 1/1] drivers/s390/cio/qdio_main.c: replace shift loop by ilog2

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Message-ID: <alpine.LFD.2.11.1405211418270.1579@denkbrett>
Date:	Wed, 21 May 2014 14:32:27 +0200 (CEST)
From:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:	Joe Perches <joe@...ches.com>,
	Ursula Braun <ursula.braun@...ibm.com>
cc:	Fabian Frederick <fabf@...net.be>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	akpm <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/1] drivers/s390/cio/qdio_main.c: replace shift loop by
 ilog2

On Tue, 20 May 2014, Joe Perches wrote:
> On Tue, 2014-05-20 at 18:37 +0200, Fabian Frederick wrote:
> > This is untested.
> []
> > diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
> []
> > @@ -411,15 +411,14 @@ static inline void qdio_stop_polling(struct qdio_q *q)
> >  
> >  static inline void account_sbals(struct qdio_q *q, int count)
> >  {
> > -	int pos = 0;
> > +	int pos;
> >  
> >  	q->q_stats.nr_sbal_total += count;
> >  	if (count == QDIO_MAX_BUFFERS_MASK) {
> >  		q->q_stats.nr_sbals[7]++;
> >  		return;
> >  	}
> > -	while (count >>= 1)
> > -		pos++;
> > +	pos = ilog2(count);
> 
> What guarantees count > 0 here?

We would already be screwed when called with count < 0. Ursula, do the
callers assure that count is positive?

Regards,
Sebastian
> 
> count may be better unsigned.
> 
> 

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