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

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Date:	Tue, 3 Jun 2014 09:41:02 +0200 (CEST)
From:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:	Fabian Frederick <fabf@...net.be>
cc:	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 Mon, 2 Jun 2014, Fabian Frederick wrote:
> On Mon, 2 Jun 2014 16:41:48 +0200 (CEST)
> Sebastian Ott <sebott@...ux.vnet.ibm.com> wrote:
> 
> > Hello Fabian,
> > 
> > On Tue, 20 May 2014, Fabian Frederick wrote:
> > > 
> > > This is untested.
> > > 
> > > Cc: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> > > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > > Signed-off-by: Fabian Frederick <fabf@...net.be>
> > > ---
> > >  drivers/s390/cio/qdio_main.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/s390/cio/qdio_main.c b/drivers/s390/cio/qdio_main.c
> > > index 77466c4..8bf9ec1 100644
> > > --- 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);
> > >  	q->q_stats.nr_sbals[pos]++;
> > >  }
> > > 
> > > -- 
> > > 1.8.4.5
> > > 
> > > 
> > 
> > Could you please resend the patch with a better description plus
> > the change Joe suggested.
> > 
> > Thanks,
> > Sebastian
> 
> Hello Sebastian,
>    Conclusion of that patch/thread was that callers guarantee count to be > 0

Correct.

> Joe suggested to have unsigned count. Is it what you're talking about ?

Yes.

Regards,
Sebastian

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