lkml.org 
[lkml]   [2015]   [Oct]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] staging: nvec: fixed few coding style warnings
Date
Am Donnerstag, 15. Oktober 2015, 11:48:12 schrieb Dan Carpenter:
> On Thu, Oct 15, 2015 at 10:39:02AM +0200, Marc Dietrich wrote:
> > > > - if (unlikely(nvec->rx == NULL)) {
> > > > + if (!unlikely(nvec->rx)) {
> > >
> > > This isn't right. You intented to say:
> > > if (unlikely(!nvec->rx)) {
> > >
> > > But even better to just remove the unlikely entirely.
> > >
> > > if (!nvec->rx) {
> >
> > why? the "unlikely" is there to optimize a critical interrupt path.
>
> The rule is that drivers should not use likely/unlikely() unless there
> is a difference in benchmark numbers.

well, we know that additional cpu cycles in this path break transfer for
unknown reasons. However, the unlikely here may be overkill. On the other
hand, I prefer not to change something here until these timing effects are
better understood.

> How critical can it be when it's
> always followed by a udelay(100)???

yes, this delay shouldn't be there at all. This is one of the timing mysteries
we still have to resolve.

> There are more important optimizations needed here.

sure. We are currently trying to move all this out into the tegra-i2c driver,
so this code block will get a major review/rewrite in the near future anyway.

Marc
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2015-10-15 11:21    [W:0.052 / U:0.936 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site